Both turn on AUTOFLUSH, so aside from the fact that the assignment is about 35-40% faster than increment, (but then you are not likely bury this in a loop :) ), they are equivalent.

Benchmark

Benchmark: timing 1000000 iterations of ass, inc...
       ass:  1 wallclock secs ( 1.13 usr +  0.00 sys =  1.13 CPU) @ 88
+4955.75/s (n=1000000)
       inc:  2 wallclock secs ( 1.93 usr +  0.01 sys =  1.94 CPU) @ 51
+5463.92/s (n=1000000)
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Holy Mid-Life Crisis

I think MitD is becoming pedantic.
Oh my gosh.

mitd-Made in the Dark
'My favourite colour appears to be grey.'