Leveling solo

[Zyph]

So I'm at level 23 CNJ and I've been hearing talk about starting to be able to solo effectively at around level 25. Where? And on what? Can anyone give me a general outline of places to solo from 25 to 50? I'm getting bored of leves, though I'm thinking I may have to do those for a while yet. I've heard GC leves are especially good, just not sure when I can start doing those.

Also is it worth it to be on the WHM job when solo or do THM skills such as Necrogenesis outweigh being a WHM?

Thanks!

EDIT: Also, what's a good stat spread?