What's the difference?

Hello Damien,
if you edit an SR preset, (edit button to the right of the choosen preset)

you'll see Separated "IMAGE SAMPLERS" section in 2 parts :
- The Adaptive AA (classic) settings will be applied if you choose into SR options to NOT use the new VBAA (And NOT Autopilot as well)
- The VBAA (new) settings will be applied if you choosed VBAA (and autopilot)

Choices really depends on your scene :
If scene if simple in geometry, but hard in glossiness you may try the new Vray 3.3 settings.
If your scene have a lot of Details to deal With (vegetation, grass...) then i suggest to set VBAA off because the AA sampler with High values will slow down greatly on this kind of stuff.

Hope it helps !

For me, but it's totally personnal, i don't use IM/LC anymore, except for flythrough animations, thanks to the flythrough optimisations in Vray.