The only starter I'm missing in Black is Piplup, so that one would be best.
And don't worry about cloning and stuff, it's easy for me to hack pokemon in platinum, if you don't mind the info being obviously wrong (date acquired, location caught, etc.) If you want the correct info I'd have to create the pokemon on my computer and send it to my DS, then trade. Which I can do too, but it's more work.