Rick Murchison once bubbled...
I own and dive both the Transpac II and BP/Wing.
If you strip away all the hype, you will find two positions on the BP/wing vs all other BC's. There are the "One size fits all" folks who are wedded to the BP regardless of the diving scenario, and there are the folks who find a narrower envelope for the BP/Wing being "best." (You may have noticed some members of the first group have a tendency to state their opinions as fact, and aren't interested in even discussing the possibility that someone else may prefer something different. It is useful to remember that no matter how strongly they state their opinion, it is still an opinion) I'm in the latter group, and so my opinion is that at this stage of the game you'd most likely be happier with a Transpac than a backplate. But I also think that if you possibly can, get in the water with both for a few dives before buying, and buy the one you like.
Personally, I don't like a backplate with a single tank at all, and I prefer the Transpac with doubles up to 85's (though the BP is just fine with any doubles). Anything larger than 85's I use the BP exclusively. (Well, there is an exception - if I'm somewhere with only my Transpac and an unexpected opportunity to dive comes up I'm not turning it down for lack of a BP just because the available tanks are 104's!)
As for the weighting/buoyancy question, for tropical diving with single tanks, you can easily find yourself with zero ditchable weight if you have a steel BP. Any wing will provide plenty of lift with singles.
Again, the best way to decide is to dive with the equipment first.
Rick
