Actually, healers have the easiest time soloing stuff IMHO, mainly because they can properly heal themselves without restrictions. Basically, for soloing content, dps are usually the trickiest because they are squishy and can't heal themselves, and need the proper strategies to quickly decimate enemies.

Healers queue very quickly for content sub-level-30. After that there's a drop in fast queuing, where for tanks, it's the other way around. A lot of low-level tanks, but there are far less tanks for over-level-30 content so they always get instant queues, while healers sometimes have to wait. Quite a bit.

Dps have the longest queue times, something which you can however easily circumvent by joining a helpful FC or LS who is willing to jump in and complete content with you.

I'd suggest going with whatever you enjoy playing the most. :]