Whichever route you follow make sure that you don't end up with the original ceramic turbines back on the motor. The answer is really determined by your power aspirations.
I too started down the mild upgrade path... Broke those...
HKS 2860's (second hand *dumb dumb dumb*) - laggy monsters that in their life in my GTR were reconditioned twice, blew an oil seal once that starved the bottom end and then threw a bearing and finally cracked one of the housings
Garret GTX35... Single turbo conversion making 700hp all day on pump fuel...
Point being if you want significant power in the future of your motor make the jump early to a new generation ball bearing, billet wheeled turbo and save yourself a fortune in the future.
Oh, and I have those 2860's (one with a cracked housing) if you wish to play with them and your bank account;-)
Sent from my iPad using Tapatalk HD