With the changes to monster health in 1.0.4 I was really thinking that grouping would be the way to go in 1.0.4 but after I tried it out (granted it was only randoms) I found that it was much worse than when I solo.
With the addition of powerful pets in 1.0.4 I find little need for tanks like monks or barbs. Even the dps classes/specs seem to slow me down because most (randoms at least) can't keep up with the dps I put out with Zombie Bears so I end up carrying the group DPS wise. To make matters worse, the mobs pass the threshold of whites dying nearly instantly and champs dying in a few seconds so certain mob types are very problematic in a team game for my semi-glass cannon WD. When I can't blow up a teleporting phasebeast when he teleports next to me, he'll end up 2 shotting me and I'll die in a team game.
So basically, I like soloing the best because:
* It's quicker since I can 1 shot whites and blow up elites quickly
* It's safer because things die so quick when I solo
* Thanks to my follower, I have extra MF while solo (which I recently read doesn't count towards the 300 MF cap)
So what do you guys prefer? It surprised me a bit but team games take longer than just soloing. The only class I don't mind grouping with is a well geared WW Barb... but that's just because they're OP and end up carrying me if their gear is good enough. I bet they enjoy soloing better as well though!