Honestly, labs are the more peaceful mbuna, but IMO they get too large for a 35gal tank. If you're stuck on mbuna, I'd stick with a species tank.
If you want to go the demasoni route (which make for a gorgeous tank, btw...I have a colony in my 33gal), absolutely no less than 12. They are very aggressive and anything less than a group of this size will likely end up with just one dominant fish left after he's killed everyone off.
As for the saulosi, I'd say 2 males with anywhere from 5-8 females.
Polits are great, but also very nasty and harder to find...plus, quite expensive. If you go that route, maybe 2 males (have to try it, you very likely won't be able to have more than 1 in a smaller tank), with at least 5 or 6 females (or 3-4 if you have 1 male).
There are a ton of different Cynotilapia afra varients, most of which are blue-ish with barring. Very pretty group of fish overall. They are some of the smaller mbuna, so the same thing would apply...1, maybe 2 males if you're lucky, with 4-6 females.
Honestly, if you want a colourful tank, do either the demasoni or the saulosi. The females of the polits and afras are very dull, mostly brown. Only the males are really colourful, and typically only one dominant male at that. The dems are the same colour for both sexes, and the saulosi have blue males (very similar to the dems) with yellow females - they make for a very stunning species tank. The saulosi are my personal recommendation in your case - they're not as aggressive as the dems, a species tank looks great with them, and they're going to be much cheaper than the demasoni.
Keep in mind with any of these guys you'll need to keep the pH up in the 7.6-8.5 area, very hard, with LOTS of rockwork providing caves and hiding spots for fish for it to be successful. Hope that helps.
