Joerg:
In a nutshell:
get a solution dyed nylon carpet. If you want the softest feel under your feet, and you can afford the additional cost, buy a Saxony. If you're looking for long term durability, buy a level loop carpet.
Why Nylon? Carpeting is made of three synthetic fibers (Olefin, Polyester and Nylon) one natural fiber (Wool). The strongest of all these fibers is nylon, and so nylon makes for the longest wearing carpets. Over 80 percent of all the commercial carpet made in North America is level loop carpet made from nylon fiber. But, most of that commercial level loop carpet is not solution dyed. Get the solution dyed stuff, and most of the rest of this post will explain why.
Why solution dyed? In conventionally dyed carpet, the fiber itself is run through a liquid dye, and so the dye molecules bind to the exterior of the carpet fibers. In solution dyed carpets, the carpet fiber get it's colour from tiny solid coloured particles (called "pigments") which are added to the liquid plastic before it's drawn into a fiber. So, solution dyed carpet fiber gets it's colour from tiny coloured particles that are suspended inside the fiber very much like the raisins in raisin bread. Nylon is a polyamide and amide groups are polar. Water molecules are also polar. Water based dyes dissolve in water because they are attracted to polar water molecules, and they're also attracted to the amide groups on the surface of nylon carpet fiber. In fact, whenever a carpet gets stained, it's usually a water based food stain and it stains the carpet because the staining molecules are sticking to the polar sites on the surface of the carpet fiber that aren't occupied by dye molecules. So, after solution dyed nylon carpet fiber is made, it is dyed a second time with a CLEAR water based dye so that those clear molecules occupy all those polar sites on the surface of the nylon, thereby making the carpet much more stain resistant by denying the staining molecules a place where they'd stick well to the surface of the carpet fiber. But, through wear, some of those clear dye molecules will be worn off as the carpet gets older, and so the carpet will become more prone to staining in the traffic areas as it gets worn out. Exactly the same thing happens to conventionally dyed nylon carpets as they get older.
But, the most important thing to remember here is that because the colour of solution dyed nylon comes from the coloured pigments INSIDE the nylon carpet fibers, you can use bleach straight out of the jug to remove otherwise impossible stains on that carpet WITHOUT harming the carpet. That's because the bleach never actually comes into contact with the pigments that give the carpet fiber it's colour because they're encased in nylon plastic. Bleaching a stain out of a solution dyed nylon carpet will probably destroy all the clear dye molecules on the surface of the fiber contacted by the bleach, making the carpet susceptible to staining in the bleached area, but you can also use bleach a second, third, fourth and N'th time to remove stains from those same areas without affecting the colour of the carpet in those areas. That is, by using bleach to remove a stain on a solution dyed nylon carpet, you remove both the stain and the stain resistance in the area contacted by bleach, but you can keep removing stains from the carpet indefinitely using bleach. And you'll never harm the carpet with bleach. So, the prudent thing to do is to wipe up liquid spills ASAP, try to remove stains without using bleach, and use the bleach when all else fails. That will ensure you have the best looking, most stain resistant carpet for the longest possible time.
And, I have no doubt that it would have occured to you by now that you can check to see that everything I'm saying is true by dropping in to any carpet store and buying one of those $2 door mat size samples of discontinued carpet and torturing it with bleach. Just make sure that the carpet you buy is SOLUTION dyed nylon. And, if you can use bleach on the carpet without harming it, you can also use bleach on any pet accidents to kill any germs left behind in the carpet at those locations. That way, you can keep your solution dyed nylon carpet smelling fresh as an Irish meadow in springtime.
Olefin fiber CANNOT by dyed by conventional means, and so ALL 100% Olefin carpets are solution dyed. Chemically, Olefin fiber is very similar to polypropylene, which is one of the most water resistant plastics there is, so Olefin carpets are naturally resistant to water based food stains. Sounds great so far. The problem with Olefin is that it's a weaker plastic than polyester or nylon, and so Olefin carpets (which is what the big box stores mostly sell) wear out faster than nylon or polyester carpets. The big box stores sell Olefin carpets because Olefin carpets are generally less expensive per square yard than polyester or nylon and people shopping for carpet at a home center are mostly looking at price. But, before I started buying solution dyed nylon carpets for my apartments, I was buying 100% Olefin carpets for them. The only reason I switched was because I wasn't happy with how long the Olefin carpets were lasting before they started showing signs of deterioration.
If you want a carpet that's going to be soft on your feet and feel luxurious, you want a "cut pile" carpet, which means that that the tops of the tufts have been cut off so that each carpet fiber in each tuft can move independantly of it's neighbors. Such a carpet is called a "Plush" carpet. Since the individual carpet fibers can move independantly of each other in a plush carpet, when you vaccum a plush carpet, the rotating brush will leave the carpet fibers leaning one way or the other depending on which way the brush was going when it passed over the carpet fibers. Some people like that, some people don't. If you don't like that, don't buy a plush carpet.
A saxony carpet is very similar to a plush carpet except that the yarns are more tightly twisted, and the manufacturer packs more of those tightly twisted yarns into each square inch of carpet to make a Saxony, so you get more carpet fiber with a Saxony than with a Plush. So Saxonies are more expensive cuz they use more carpet fiber so they cost more to make.
If you want the carpet to last the longest, or you're concerned about someone in a wheel chair being able to roll over the carpet easily, get a level loop carpet. Most people would consider a Berber to be a kind of level loop carpet. There's a natural resilience to a loop that results in level loop carpet standing up better to high traffic than cut pile carpets. To my knowledge, ALL commercial carpet is level loop carpet cuz commercial carpet has to be long lasting.
And, the best way to get the longest life out of a carpet is to vaccuum it regularily with a good quality vaccuum cleaner. There's a popular misconception that shampooing a carpet will get it cleaner than vaccuuming, but that's not true. That's because as soon as you get the carpet fiber wet, you create something called "surface tension" on the surface of the carpet fibers that keeps dirt stuck to the carpet fibers. Next time you're at the beach, try cleaning sand off of wet feet and dry feet and see which one works better. Really, a vaccuum cleaner is meant for cleaning SOLID soils out of carpets, and a carpet shampoo'er is meant for cleaning liquids and dried up liquid spills out of carpets. They're different tools meant for different jobs. If you intend to shampoo your carpet, you'd do well to vaccuum it thoroughly first to remove the solid soils, and then shampoo to remove the dried up liquid spills. Vaccuuming after you shampoo is a waste of time.
There, now you know more about solution dyed nylon carpet than most people. And, most people would buy solution dyed nylon carpet if they knew what they were paying extra for. They don't, so often they go to big box stores to buy Olefin carpet at half the price. And, truth be told, if I couldn't buy solution dyed nylon carpet from my local carpet store, I'd buy Olefin carpet from a home center and just replace it more often. (I install my own carpets.)
Now, about paint...