I've just started with this as well, bought the slim line 15pcs set. I haven't tried the 'normal' size versions and as I live in Norway I doubt I've encountered any 'normal' size locks. Some of the ones I've tested barely even fit the slim lines, like the door locks around the house.
True, they do tend to curve a bit if you treat em rough but they bend just as easily back and don't seem fragile at all to me. Unless you got feet for hands I think you should go with slim line. Presuming you'll encounter some narrow locks in the future.
