[Bolix]

I think that soloing is faster xps for me (cleric non-twink). But you need to get a good soloing spot and have your technique down right. And soloing does allow you to AFK more to do real-life things.

Downsides are though:
1. Alot of time spent sitting down medding, which is really pretty boring.
2. Not very sociable, you can't talk to group mates.
3. Boring as you are doing the same thing to the same few mobs.
4. Can't go to interesting places or camp interesting things.
5. One dimensional.
6. Don't build up grouping skills (how do I interact with various other classes, what synergies can I develop, how do I work as part of a team).

If I have the time, I think it is better to group and I can understand the frustration of a non-twink having a hard time to get xp whenever the twinks are soloing all around them.
But ultimately its the choice of the player to group or solo