Define "issues"?
They all have the same unit construction engine/gearbox, so it's a crap shoot there, I guess.
The B5 and C5 require fork removal to change the fork oil. The G5 doesn't, so buy the G5. Or at least it didn't used to - do I recall a G5 owner recently finding they had to remove their forks to refill the oil? Ok, forget the G5...
They all seem to come with a bad chain. If you want to change it to a good quality o-ring chain, you'll have to change the drive sprocket on the B5 and G5, which requires removing the right-side engine cover; the C5 comes with a larger size sprocket (due to the smaller wheel size - do I have this right?), so it's a much easier job. So buy the C5. But as Scott said, a few of the early versions of this model had some stability problems, so better forget the C5...
I have heard many claim that because the B5 is the old bullet frame, there are many more accessories available for that model, so buy the B5. But wait, I just have not found that to be the case - at least through nField Gear and Hitchcocks. There may be more available through the Indian suppliers, but I've never had much luck communicating with them. Forget the B5...
Umm... shoot.
They all
look different - buy the one that makes you happy!