For the basic models (AN-E/LX, AN-J/LX, SPe versions of both, HEMP versions of both) drive units are the same. Crossovers and cabinet dimensions are different and the AN-E models are a little more sensitive, but only by 1dB or so. Both have the same kind of 'Audio Note(UK)' sound, so if you like the one, it's probable you'll like the other.
There is no 'HE' version of the AN-J because the HE bass drivers are physically too large for the J cabinet unfortunately. There are also no 'Signature' (outboard crossover) versions of the AN-J.
Contrary to popular belief, both play happily with pretty much any amplification you wish to use them with. There are quite a few happy Naim users who have E's and Js, and the combination works surprisingly well.
Martin.