I enjoy SMBC for its ability to create intelligent non-sequiturs, often in 1 panel comics. The art style is fairly crude, but the writing is always top notch. The author also does decent sketch comedy sometime.
I used to like XKCD, but got sick of the faux intelligence that dogged most updates. You know what the Michelson-Morley experiment was. Well done. There's no reason to make a comic about it. Although, at times XKCD has been really good i.e. "there's somebody who is WRONG on the internet", but most of the time it seemed that it was just referencing some obscure experiment or equation with little comic effect.