Tempest has better meterless damage by about 5%ish across all combos, has better pressure with +7 EX hat, and has better oki with orbiting hat.
Buzzsaw has better neutral with his low hat zoning, up hat to anti air, and straight hat that you can run behind and convert with combos if the straight hat anti airs. Also better mixups, but with practice B2 low hat or B22 can be fuzzied.
It's hard to say which is better honestly, just depends on preference and also depends on what character you are fighting against. If you can't hit the hat spin 44 link consistently for that great meterless damage, then Buzzsaw is for sure better for you