That question is still being debated, but mostly boils down to:
T-1 if you really need the better up-time and want to avoid possible slowdowns durning "peak" loads you could get from cable.
Also T-1 should have a higher "fix me now" than cable in the event of unavoidable problems.
But most people that have switched to Business Cable, seem fairly happy with it. Though ComCast does take some flack about some of their policies.