Personally my favorites are E-Lo (he used to use the name Kwandaoren66) and Nbz, although that used to just be because they were the only ones I watched; after keeping up with them for a while I saw that Nbz also did Fire Emblem videos (and he was part of what motivated me to play it myself, love the series now) and I ended up watching those more often than his battles haha.
I really enjoyed E-Lo's picture in picture narrations, cause I thought it was unique and gave something else to look at while the battle was going on. I remember one time he took out a Blissey with Perish Song from 100-0%, made a sandwich on screen and started to eat it while its HP was dropping and it was probably the funniest thing I've seen him do lol. I also remember way back in the day he thought there was a ghost in his house and he streamed his attempt to try and communicate with it, and it was super late night so it was less people and more personal...ish. I guess. His TCGO videos were also pretty informative I think, as someone who tried maybe once to actually play it and never again.
...And then there's time he flipped 14 heads on like the first turn of a game with an Iron Head and won by popping the guy's only Pokemon on the field in one shot.
I made my tumblr a long time ago for the sole purpose of following E-Lo; he's super chill and I got to talk with him a couple times, if only very briefly, about a music artist and more recently about an anime I wanted to start (and have since started). He also added me on skype for a pokemon tutoring group he was starting (sadly it didn't go anywhere) so I like to pretend that matters.
And, of course there's the obligatory Shofu since I started watching him when I heard he started playing Reborn. I've been watching his Sm4sh videos more recently, but I don't keep up with his battles too often.
Can we count Glitch because her remixes are amazing? Yes? Okay, her too. She's in the same boat as E-Lo kind of; seems really cool and I follow her on tumblr where I make (less successful ;-; ) attempts to ask small questions just for the sake of trying to talk with her
EDIT: YO I FORGOT MARRILAND I'M SO BAD LOL the Marriland forums were directly and indirectly a HUGE part of who I am today as absolutely cliche as that sounds- it's where I met Inuki and challenged him to a battle and eventually was invited to join his old forum of like two people that became our hangout for at least the next couple years yada yada best friends blah blah blah here we are now EDIT2: found the sandwich video
EDIT3: TCGO hilarity