I have a L28 AR/Energy Blaster, as well as a L24 Ice/Elec Blaster.
Assault Rifle is definitely faster to level in "AoE" situations. However, it's very boring compared to the gameplay of Ice. The decision-making part of AR is "where do I stand to pop off flamethrower?". For Ice, the combat is much more dynamic, forcing you to choose real-time who to Freeze, who to concentrate firepower on, etc.
Playing Ice without the Holds and trying to focus on its relatively weak AE attacks is not something I'd really recommend. The only time I use my AE attacks on the ice blaster is purely when I'm in a group with multiple blasters and we're all AEing.
Ice is superior in terms of single-target damage, and you get some great utility out of the two holds. AR is far superior in AE damage. It's a pretty good tradeoff.
In the end, at level 50, I want to have had a good time getting there. Pressing Build-Up/Flamethrower all night long is not necessarily my idea of fun (not after the first 10min, anyhow).
