Which is better? I need Lipo technology.

[Batfish]

I use both the 3200 and the 6400 FMA BalancePro packs. I can tell you that both Tower (Great Planes) and Horizon Hobby ship them ground only. I don't know about other shops, but you can be sure that if those two are doing it that there's some regulation about it.
On a performance note, the lipo batteries pack serious punch and sustained performance over nimh. My example is the 4wd buggy class at my local track. I'd been running my xxx-4 with a Peak Dynasty 19t spec motor and 6-cell IB3600 or matched 6-cell GP3300 against a 10t double xxx-4 for a couple weeks. Most of the time I could keep up in the technical parts of the track, but I was easily out run in the straight. My 3200 BalancePro pack came in, I charged it up, and now the 19t can match the 10t motor in the 100' straight.
The big difference is that the lipo packs don't drop voltage under load like the nimh do. It's also nice that it weighs less.