Best actors on the show?
I'll preface this by saying that I genuinely don't feel like there was any weak link in this cast (particularly amongst the main cast), and I think they all did really excellent jobs with their characters :) That said, I always enjoy seeing people's opinions about acting performances since it's such a subjective thing!
For me:
William Daniels kind of goes without saying- he's basically on his own level of awesomeness, and he never missed a single beat as Mr. Feeney.
Of the younger cast, it's always been quite an even tie between Rider and Will in my book. They both had that knack for being able to float seamlessly between hilarious, adorable, and heartbreaking. And although the writing did contribute to the range they were able to show, I feel like it was material that could have easily skewed too maudlin (in the case of Shawn's storylines) or too cuckoo to be funny (in the case of Eric's storylines) if handled by other actors.
Now granted there was really no saving Eric's character in season 7, but prior to that, Will had this way of being hilarious while still always grounding Eric's aloofness with those moments of real, deep thoughtfulness and sweetness. I feel like in the hands of a lesser actor, those genuine moments could have easily still read false for a character as silly and quirky as Eric. But the second those moments came along with Tommy, his parents, Mr. Feeney, etc., Will sold them so naturally that you instantly DID see him as more than just the wacky brother always getting into ridiculous situations. And yeah, just in general he is the most hilarious
And with Rider, while I've seen some comments around here about Shawn's getting "annoying and whiny" by the end of the series, I actually never did feel like he got there, in large part because Rider's performance was so good. He had such a natural vulnerability about him that never read as overdone or "look at me, look at me, I'm moody and upset!". It also helped that all of the emotional issues Shawn had were things that we'd seen building up since season 2, so when they finally boiled over, it did feel earned from a writing perspective, but still I think Rider grounded it really well with his performance. He had a good handle on when to let it be more subtle and internal hurt, and when to let it be that big emotional release of all the pent up anger and hurt (i.e. in We'll Have a Good Time Then). And then at the same time he could keep up with the best of them on the comedic front too and had excellent chemistry with pretty much the entire cast.
Again, though, the whole cast was really great! They all had their moments of showing off really wonderful acting chops throughout the series :) Maitland Ward probably left the least impression on me acting wise, but she still wasn't bad so much as Rachel as a character just wasn't terribly engaging like the others were.
Oh Bambi, I cried so hard when those hunters shot your mommy. - Kurt Hummel