When I started competing, my main throw was the 888 ('07). I used these for 3 years. they had it all. fast, long spinning and stability. I got away from them. 
I pick up an 888 from time to time. Not a big fan like i used to be, but its good to know I have undersized yoyos around to play from time to time.
My first yoyo was a yuuksta and my second was a 888x. I didnt realize they were undersized until I got a Northstar lol Now I prefer a full sized. But I believe the undersized yoyo helped my control a lot, and I still like playing with them time to time.
I love undersized yo-yos, and I have a case for tiny yo-yos too. My favorite undersize yo-yos are MMN and Dingo by One Drop:
I think these are all the ones I have under 53mm:
Yomega maverick (black)
Yomega Dash (blue)
Yoyo factory mighty flea (silver 2011)
Yoyo factory One (black, version 1.)
Yoyo factory Popstar (blue) (purple)
Yoyo factory DV888 (red)
Yoyojam Micro Mo (green)
Yoyojam Hitman Pro (black)
Yoyojam SR-71 (blue)(nickel)
Yoyojam X-Con (blue)
Yoyojam Mini Motrix (red)
One Drop Markmont Next, Nickel
One Drop Markmont Next, Soda Blast
One Drop Dietz (nickel,signed) (YYE Edition)
One Drop Dingo (red,yellow,orange,blue,nickel,blue/black c.blossom)
One Drop Y Factor (nickel)
One Drop Lab Experiment #1 (red)
One Drop Cafe Racer (black)
General Yo Entheos (yellow)(blue/green)
General Yo Ministar (black/pink) (black/purple)
General Yo Hatrick
Tom Kuhn Pocket Rocket (silver)
3yo3 Omnicron X (raw silver)
C3yoyoDesign DiBase (black bead blast) (blue bead blast)(purple)
C3yoyoDesign Token (blue/black)
Aoda little (brown)
Shinwoo zen 4 (silver)
Dream yo pixie (silver)
ILYY St. Eel
ILYY Noctu
Oxygene 5 (raw)
Spyy Spyder II
Spyy Supra (gold dust)
Monkeyfinger Evil Yo (YoyoExpert Edition)