1) is the older version. 2 & 3 is newer ones, with added head vulcans and somewhat 'slightly' improved knee articulation (from 90 deg to er.... 100 or 110 degress i think)
if u have the money try get the cage ver, it's a nice accessory to have

for more detailed pic, can go dalong.net to see
for more detailed explanasi, wait for parody or starghazzer to break it down to u
for biased opinion, ask me, i'll ask u to buy MG Sinanju

I asked this question in the previous version of the thread too. 

I have bought the one with the MS Cage. It's a pretty cool kit, despite the high price.

Movements and Flexibility:
ver.Ka lacks in articulation, which the leg cannot really bend that far, it's kind like a brick (most youtube reviews says that)
in the other hand, the one with the cage has better articulation, they improve it and made it MUCH better than the ver.ka.

Details:
ver.ka has nice decals.. no doubt about that. But you can buy the ver.ka decal from a specific website. The ms cage has nice details and a place to store the unicorn's weapons and stuff. But, I dont like the fact that they changed the lightsaber from pink to blue.. to match the HD color. 

Much worth getting:
The unicorn with ms cage of course.. if you have the money la 

Hope I helped. 

The OVA version is without the cage la obviously. It's only the gundam.
I'm not sure about the articulation, details or whatsoever about the OVA one, but I can tell you, the one with the MS cage can do a lot of poses, gimmicks and stuff.
The knee of the MS cage and OVA one have better knee articulation than the ver.ka thats for sure.