I would personally say go where the value is. The one problem is that if you have Rudi and Carson or if you have Boldin and Fitz, you are in some trouble when that team's bye week comes around. I've had McNabb and Westy both on my team a couple of times though, and it has been pretty successful.
Teammates are a minor concern to me but QB/RB and WR1/WR2 combos are ones I do try to avoid. Generally its hard even when you've got a great combo to have both Wr1 and WR2 on a team get 100 yards receiving. It's just hard because teams will find the guy to exploit in the secondary, or the WR getting 100 yards is likely having a great day, or just the uncovered one, so he gets more throws. Of course, you could argue that this is playing it safe. You know Manning will have a good game at worst, so if you could get Harrison and Wayne at least one should go for 100+ yards. Also, running heavy days are typically not great fantasy days for QBs, so QB/RB is counterproductive in that regard.
Of course I wouldn't forgo a Harrison/Wayne combo to have a Harrison/Plaxico combo, but on equal players I'll try not putting all my eggs in one basket.
I try to avoid the WR1 and WR2 from the same team, but other than that, whatever....
I think the QB/RB teammate combo is criticized unfairly...If you think about it, you're gonna get a piece of the pie every time that team goes in to score no matter if it's running or throwing....The only time that combo doesn't work is if the entire offense is bad....That's why it's better if you've got one of the elite QBs (Peyton, Brady, Palmer, Brees, Bulger, McNabb) and their RB counterpart...In fact Plindsey (a moderator here at the Cafe) won an expert league using this same strategy of Bulger and Jackson...
I personally don't like the QB-RB combo unless it's a pass catching RB. If it's Bulger-Jackson, McNabb-Westy, Phillips-LT fine but otherwise, no. Too much of a limitation on your team's explosiveness. Now, the QB-WR duo is actually something I target (from passing teams). Won a SB with Hass-Jackson. This year, I am targeting Bulger-Holt or McNabb-Brown.
I personally think that this should affect your draft decisions extremely minimally. I go on my projections and if I get two guys on the same team then I'm drafting them for their projected stats, being on a team won't change that. Of course, making good projections means that all the players on one team have stats that add up to reasonable team averages and you don't project breakout years for every player on a team equaling absurd totals radically different from the team's stats the year previous.
It makes no difference other than the streakiness of your team. Having teammates means that on good days for that team, you'll win. On bad days for that team, you'll probably lose. With players on different teams, you diversify the risk more.
Other than that, it makes no difference.
"Cincinatti leads the league in 'Johnsons'" - John Madden
Since the other one was older, I'm gonna stick with the new one.
I personally love having teammates. Especially in high scoring O's. For instance last year in my 2 qb, PPR league, I had the luxury of having SJax/Bulger AND Westy/McNabb. All those dump offs to the RB's really added up. Palmer / Rudi would be a good one, even tho Rudi is non existent in ppr, but you get the idea. Brees/Bush would be one I would be targeting as well. Even for WR's. I mean if you have a stud WR, and their qb to go with them, why not double up the points? Of course, this is IMHO. Good luck!
10 team / Keeper / 2QB 2RB 2WR Flex TE DEF McNabb/ Griese / JP / Clemens SJax / Gore / Julius / T.Jones Braylon / B.Marshall / Cotchery /Hackett Gates / Olson TENN