shakib better with bat, ashwin with ball. as said they play for different teams with different standards and different roles. whilst both are the main spinner shakib is also a vital batsman, difference with ashwin is that ashwin isn't a vital batsman, he might play a vital role as an all rounder but you wouldn't consider him specifically as a vital batsman. he generally bats at 7 or 8 and he's not expected to make runs as a batsman would whereas shakib bats higher and is expected to be a main cog in the batting and is expected to make a greater amount of runs for his team.
All Time Test XI: 1 Hobbs 2 B.Richards 3 Bradman 4 Pollock 5 V.Richards 6 Sobers 7 Gilchrist 8 Miller 9 Procter 10 Botham 11 Warne