I've only seen a couple of fire/storm controllers but they were awesome to team with.
The Stone/Stone tank you'll probably always be able to get a team with but IMO the Fire/Storm troller will speed up the team more and thus level quicker
"Well, they found my diary today.
They were appropriately appalled
at the discovery of the eight victims
They're now putting it all together.
Women wrapped in silk
with one leg missing
Eight legs, one body, silk,
spider, brilliant!"
Go for the toon you have the most fun with. If it was me I would rather choose the troller any day. (I am not boredom-resistant enough to play a stone/stone tanker, let alone solo one.)
I do not know fire/storm, but I know fire/ and /storm enough to say that the combination will hit 50 with no problems whatsoever, even if you have to solo some amount of it.
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
Thanks guys i use the controller then 
I think the stone tank will be painfully slow to level up solo.
Whichever toon you play, the most important factor will be how much time you spend in a team. You can't beat an 8 man team for XP.
Good luck.
Hay all.
I got 2 heroes both level 38 but not sure what be the easiest one to try and get to level 50.
Keep in mind i guess i would need to solo a lot incase there not groups.
I have fire/storm controller and stone/stone tanker.
Thanks for any advice