While I've never used it myself, Reaper is popular with some professionals. It can use AU or VST plug-ins and seems to be pretty full featured. The major comlaint I always hear about it is since it's so customizable, it's a bear to get it up-and-running.
I have heard that people post key layouts that follow the standards of most major DAWs, so you might start looking for those. Sorry for the second hand info, just going by what I've heard from a few very talented pros.
Abelton always has seemed clunky to me, but my recording experience mostly comes from an engineering and production background so the analogies are probably not geared for someone like me.
Logic might be a good choice since it will probably receive updates to flow with OS X updates quicker than others.
Personally, I use Pro Tools, but if you plan on using a lot of VIs at once you'll probably need to also invest in a plug-in server like VSL's Vienna Ensemble Pro.
As to the loop vs. no-loop thing: Use whatever gets the gig done at a high level. I usually just write and play parts myself, but have no problem using loops in a production. It's not disrespectful to the craft to use whatever tools you have available.
