Hi there, Trevor! I agree with Kreston - gray is better. I've primed figures with white primer and missed flaws on the figure simply because of the stark color of the primer (it's WHITE!). However with grays, I've found it easier to see flaws - seamlines, pits, slippage, etc. - with this color. There is nothing worse than being well on your way through painting a figure only to find a slight little seamline on the figure. Yyyyyyyyyyyuck!
As to which primer is the best, well, I know for a fact that a lot of guys in this hobby go with gray auto primer. Why? It's fine enough to not obscure any detail, it's cheap (regularly $3/can compared to Floquil primer that runs you about twice as much - I kid you not!), and it's readily available just about anywhere you look at.
No matter what you do ... for God's sake, do NOT use silver paint as primer. Trust me, it sucks big-time.
One last thing: do not spray too much primer on the figure. What I do is simply spray the can and run the figure through it a couple of times on all sides to give it just enough primer. Just remember not to overdo it. If you don't get the complete coverage onthe first pass, then give yourself time to let the paint dry and go through with a second coat.