Alex, thanks for the link to Bob's Benches. It's very informative.
Personally, I use two front, wooden vises on my bench, one centered on
the side & one centered on the right end. (I'm right handed.) I have
peg holes for 3/4" dowels in the bench top for them to push against. I
also have them 1/2" above the top of the bench. On the front left leg,
about half way down, I have an iron vise with wood padded jaws. I
had to redo some windows & found it very handy. I can also put a board
in it to pick up the end of a long board in the side, front vice when
planing. Both my front vises are home made, single wooden screw with 2
stabilizer rods. I made the side one extra long & sometimes have to
put a shim on the far side if I'm clamping on just one side. It's wide
enough that I can usually put a vertical board between the screw & the
stabilizer rod without a problem. That one is made of maple. The end
vise is made of walnut.
They work pretty well for me. I like them sticking up over the edge of
the bench, too. Occasionally, I have to pad a board up a bit, but
usually I don't & I get good, solid pressure across the top of the
bench. I did screw up & have the screw too high on the side vise
(higher than the stabilizer bars. That can be a bit of a pain. Also,
that vise has round stabilizer rods & they aren't as solid or steady as
the square ones I have on the end vise.
I used a 6" quick release iron vise for years as my side vise, which is
the one I primarily use. I liked it, but it just wasn't wide enough.
I that vise to be at least 12" wide. My current one is 20", which is a
little too long, I think. Next one, I'll probably drop back to 16"
Also, the quick release had the disturbing habit of picking its own
times to release. It was old & worn though.