Which one is the easiest? Hmmmm Interesting question. Sounds like you don't have much experience in video production, but you want to get started.
A few months ago I was in the same situation. Maybe this will help. Ok, let's say you have no experience with women. Would you rather find another inexperienced woman, so you can learn everything, for the first time, together? Or would you rather find a pro (a hooker) who can teach you everything you need to know? I would consider the GL-2 and VX2100 the virgins of the group and the XL1/2 and DVX100 the hookers (but one you could take home to Mom and Dad). ;D
I have the DVX100 and it has taught me ALOT. I have yet to find any limitations. The XL2 is comparable to the DVX100. The GL2 and VX2100, I would consider, the easiest of the group. IMO.
How much of each? If primarily home and vacations, there's not much need to go past the GL2. You wouldn't want to lug around anything much bigger than that, anyway. I never take my DVX on vacations.
than go with the dvx. I bought a gl2 because I was a newbie in dv world but after few weeks, I realized that I didn't do the right choice so I sell it and buy a DVX. When I go through something, I go very deep, always further. If you're like me, than go with the dvx.
The GL2 is a fine camera. Good optics, good picture quality, relatively low noise...it's just very "consumer" in terms of it's controls.
If you're doing vacation, home video and documentaries...the GL2 is perfectly fine (although you'd want to look into getting an XLR Mic preamp to add to the audio features for a documentary).
If you are seriously interested in short films, then you'd want to look more seriously at something like the DVX100/A or perhaps a used PD150 if cost is a concern.