Corey,
Since the '70s, I've sailed with every known design of junk sail, and also a number of different wingsails. My first sail under junk rig was aboard Pilmer, with a flat HM sail.
My Sadler 25 Lliutro had two different wingsails, rigged with all kinds of batten experiments. Ivory Gull has a combination of hinged battens and cambered panels. Tystie has had three different junk sails, all with cambered panels with varying amounts of camber; and wingsails with two different sets of battens.
From the perspective that that experience has given me, I could now only ever recommend flat sails to a sailor with a very laid-back, relaxed style of sailing, who was about to go for a trade wind circumnavigation. For inshore sailing for leisure and pleasure, quite a lot of camber is the way to go - say 8 -10%. The further offshore you go, the less the camber that is necessary, but I feel that there should always be some camber - say 4 - 6%. More camber means a bit more work to do in setting the sail, but more rewarding performance.
Junk-derived wingsails, made the way I design them, are actually easier to sail with than pure junk sails, having no yard hauling parrel, and ideally no luff hauling parrel. I'm in the process of making a new single wingsail for Tystie, and I can tell you from current experience that it takes a very great deal of work to make one. So that's a trade-off: more work up front in the building, better performance and easier sailing later on.
I've decided that I much prefer the approach of having a flat-cut sail and some form of articulating or shaped battens that put in the camber, over cambered panels in the sail and straight battens; but that's a personal choice.