Senior's TF work is awesome, but I'm also a big fan of Andy Wildman when it comes to giant robots fighting.
best artist ever though I don't think I could choose, different artists work on different things. JR Jr's Spider-Man is by far my favourite, but his Iron man and Thor for the upcoming Avengers book look awful. Whereas Olivier Coipels work can often be sparse, but his Thor work looks amazing and fits the book perfectly.
David mack makes lovely, lovely pages. I like the scratchy, gloomy stuff by Maleev, Jock, Sean Philips and the like. Romita Jr does great Spidey and great Punisher. Gary Frank's Superman is great, as is Amanda Conner's Power Girl.
sometimes it depends on whats been drawn and if it best suits the story, the art of somethings could be considered crap in retrospect, but is awsome for that particularity...
I've been thinking about this and after many days of mental gymnastics, league tables, point allocation and some underhanded attempts at bribery I've decided that The Best Comic Artist ever is/was...