I don’t have an indepth knowledge, but I do a little about Red Bull’s system. They used rear pull-rod in both 2009 and 2010. This partly why in 2009, although Red Bull didn’t have a double diffuser to start with, they were able to improve dramatically (with respect to Brawn) in the second half of the season.
Rear pull-rods allow a greater degree of flexibility when it comes to aerodynamics, particularly the diffuser.
McLaren traditionally (for the last few years) use a much firmer suspension than, say, Red Bull or Ferrari. They’ve used push-rods for the last two seasons (at least), so I’d guess they’d stick to it again for 2011.