Hi and welcome to 2+2
Bit of both for me. I usually click the shortcut buttons and then adjust manually if necessary depending on what I want to achieve.
So for example, if I have whiffed with my AK and the flop is really dry, I will click the half pot button and then look at the amount and maybe add a bit more manually to make it look a bit more to villain.
I play mainly SNGs at the moment where stacks aren't very deep, so bet-sizing is pretty important IMO and a small adjustment of even just 10-20 chips every now and again can be significant.