Grant Morrison's run.
Claremont's original run ONLY.
The original New Mutants.
Whedon's Astonishing if only because it was extremely popular (I didn't fancy it).
Gillen's Uncanny and his AvX:Consequences. Short run. Very good run.
I love Rogue and Psylocke more than any other characters so I tend to flock wherever they go.
Bunn's Uncanny X-Men was also pretty good.
Avoid Bendis' X-Men. That run was running in circles and pretty much made a mockery of any continuity.