Why does one choose one over the other?
Why wouldn't you use a small light grunty sail instead of a bigger flatter sail that produces the same power?
The reason I've heard is that bigger flatter sails have more range. Can give you better average speeds over time, but smaller gruntyer can be faster in the gusts.
Interesting question. I am coming from the wavesailing perspective....
as a big guy (95kg) I've always had powerful wave sails. Then one day I heard a pro instructor fella say "you can only use one sail at a time" , meaning really is it that different (on any given day) if you use, say, a 5.5m flat bladey sail or a 5.2m deep powerful sail? In the same wind they will make the same power. Arguably the flatter lighter handling sail will be better as it will make same power but depower easier for waveriding and tricks etc.
I tried NP Zones and they feel sooo nice compared to a Simmer X-Flex I've bene using for years (powerful X-ply with vinyl window).
I am now caught in the debate of what feels soooo sweet on a wave, vs. what is downright indestructible. Better sailing and pay more with shorter lifespan.... or almost as good sessions and longevity
Yes 
seriously just being objective, they feel better (for me) but I dunno if I wanna pay more for something that won't last as long
IMHO
Personally hate with a passion flat wave sails find they have such a narrow wind range in comparison to a sail with a bit of grunt in them.
Have tried a few different types in past but have found like the searches and alpha's with the better range. Just my preferences.
Please note, there is very little finesse in my sailing, generally brute force and ignorance.
Flat sails are possibly less rangy, but smoother power delivery in gusts.... don't get reefed forward when you least need it ?
It is not justt he flatness I like the foil (skin) tension now I think
still got 05 zones and their going strong. i give them a thrashing. who says their weak?
I have 2 x '05 Zones and a '08 Zone. All of them have a hole worn in the luff tube where the mast rubs in it when inserting ... about 3/4 of the way up.
I have 6 x '04 Simmers with no discernable wear, no stitching problems, nowhere near wearing holes in them.
I am sure if you fall on a sail like in a catapault, or run them thru the rinse cycle in a wave, they are all similar strength when new. But it is pretty bad when a sail gets a hole worn in it just from rigging..... and even worse when 3 model years later the manufacturer has not rectified it!
Even little things like the Simmer bags are still fine, all the zips work, no wear. The NP ones have holes worn in the bag, zips stuffed up long ago and the graphics fell off (who cares really, but still...). All for an average extra cost of $180 each 
But I like the vibe and they feel nice to me so what to do??!!!!
wouldn't a big flat sail give better upwind performance than a smaller bagged out sail?
i agree. no holes in luff sleave of any of my zones and i start pull it on from the top as grumplestiltskin said. lazy rigging gives holes
I've lazy rigged all my sails since the year dot 
And Haircut "wouldn't a big flat sail give better upwind performance than a smaller bagged out sail?" ............. I agree. I even find that when I can barely barely plane and have minimum downhaul on a sail (but still enough d/haul though) for max power, I find when I do get going it will barely go upwind. I downhaul another 5mm and it takes another couple of pumps to get planing and then it will go upwind OK.
But it doesn't b*gger up Simmers or Severnes in my experience...... 
One year of lazy rigging a Zone = hole. 5yrs of lazy rigging Simmer = still fine.
oh and I am still looking for a 2003 -2005 Zone 4.1 or 4.2 and my wanted ad has resulted in NIL. Anyone?
