Interior walls - to prime or not to prime?

Hi,
I have a house about 18 years old and now consider to repainting some rooms and hall. Walls are already painted using latex paint. I will be painting on to also using latex paint.
Question: Should I prime walls before painting? I talked to Benjamin Moore sales rep, and he told me yes, I have to prime first and then apply 2 coats of paint. Some other places said that priming is just required if painting over darker color. So if I am painting over white wall with some new yellow color paint should I prime?
Also, If I consider buying Benjamin Moore paint, which paint should I get. I was told that they have top line, mid line and low line paint. Top line is more expensive (about 8 $ more) , but I was told it is easier to paint.Whould you recommend go "top line"?
Anyone knows software online that would let me change wall colors of my room photo?
Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
without seeing what your walls look like, it's difficult to advise, but if they are in sound condition, and relatively clean (as in a non-smoking and low grease environment) then I would think with a good (not even necessarily the top of the line) paint, you could get by without priming.
That said, is the gamble worth the extra few but and time for priming? If you prime AND use a good quality paint, I would think it unlikely you would need to prime AND two coat the finsh color unless you were going over or applying an extremely dark color.
My case in point - I recently painted over a deep red (called Geranium, so you get an idea how dark!) with a light lavender. One primer coat and one finsh coat and I was done. I use Sear Easyliving.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If the old paint film is in good shape you don't need to prime. However if in doubt prime.
Here's a tip - Have the paint store tint the primer to half the formula of your topcoat. That way you'll only need one topcoat unless you're using crap quality paint.
I always use top shelf paints but I've heard that BM's contractors grade paint is nearly as good as their top shelf brand.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yellows cover the least, priming is only necessary on gloss, or dirty stained walls. Use the better paint but yellows often need 2 coats.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

the heaviest and have better covering power. This was pointed out to me years ago by a different paint manufacture. You only want to paint once so use the best. However 2 coats are best to be sure of even coverage. W W
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

it doesn't matter so much.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don't know about on-line, but you can get a CD at any Home Depot from Glidden that will allow you to "paint" the walls in your own home photos.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.