I just got my epoch a couple days ago so my opinion might be swayed a little. So, get ready to read, maybe, i have work soon. So the good choice out of the options you have put forth depends on how much room you have. In my opinion, if you have room to play with, the epoch is the best choice because of the proportional steering with the front wheels turning and the back wheels driving. Also on another note, if you do not have alot of room to work with, the digi Q is a good choice...although make sure you get the special controller otherwise you need more room because you can only change between two settings. Also with the digiQ it doesnt run well on carpet so if you have a nice wood floor or a pretty big table/ desk they are great. The bits are just fun to play/work with, except that they take a little massaging before you get them to run fast. The epoch and the DigiQ run fast from the start. so here is the order if you have a bunch of room
1)Epoch
2)Digi Q
3)Bit
if you just have desks to run on here is the order
1)Bit
2)Digi
3)Epoch-probably not though
oh and if you want to see the size difference there is a pic on someones gallery here, but i came up with a good comparison you can do at home:
Digi-Q= about two quaters next to eachother (touching)
Bit = about two and a half quaters
Epoch = little more than 4 quaters in length, or two AA batts lined up