Maxon is the original TubeScreamer.
Bear in mind that an OverDrive pedal is not a distortion pedal! I would never use this alone to get a good distortion - if you're searching for that, go to a diferent pedal all together. Distortion that comes from the amp is the best one you should always rely on.
What OverDrive IS used however for .... I use this in cooperation with the distorted channel of my amp, to give my guitar signal a bit of a boost. Much like a compressor, it also gives your playing more edge and sustain, and you don't have to hit the strings as hard as to get that kind of a sound otherwise.
The sound of the Maxon OD-9 is very transparent and doesn't alter the tone of your amplifier that much (the Tone option does very little but adds some small colour to your sound) which is actually perfect for an OverDrive pedal.
I pretty much use this ON during all the times so I get teh most out of my distortion sound, but it could also be used as a booster just for leads and solos, giving you more compression, sustain and grip to the sound.
This is Maxon's original model with not that many extra features and there are several different ones with more options (that's why -1 on the features) but it all depends on what you require.... for me the more simple, the better.
I've also tested this in comparision to Ibanez's tubescreamer (the more recent one, not the original with the Maxon chip) and I think the Maxon chip sounds much better.
So hail the original TubeScreamer!