I find spreading things round all three alliances helps me out because I don't really mind where the miles go. This weekend, I'm in India. Flying BA would have given me BA Gold, and flying Skyteam would have given me KL Platnium, but unfortunately neither had reasonably priced options, so I've ended up on Lufthansa / Swiss with *A where I don't really need the points... but figure they will get used eventually. So each year, once I've achieved a decent enough level of status on all three alliances (ie: a level providing lounge access), it's all about price and convenience.
I guess it depends on your priorities. The longhaul trip I do most often is Texas-London. It's never less than a one-stopper from AUS, and I discovered many years ago that it's easiest if I leave as late as possible and make the connection as close to AUS as possible - that way I get the longest sleep time eastbound when my body clock is most ready for sleep. Westbound I arrive ready for a good nights sleep.
If I take different route to get a better class of travel or a "nicer" airline, but I have to leave morning instead of late afternoon, make extra stops in Europe or the East Coast, or I have to spend 3+ hours in a US domestic clunker, that rapidly nullifies the gain, to the point where I'd seriously figure the heck with it - I'm going to be tired and uncomfortable, I might as well just take Y on the most direct routing.
As they say around here, YMMV.
PS - I forgot to say earlier, I agree with everyone who commented on the comfort of the WT+ seat - the space is good, the seat isn't - it's hard to understand why BA didn't fix the padding years ago.