Turbo help
 

I've read many of the other turbo posts asking for help, but i wasn't satisfied. I was wondering which turbo is best for power: The HKS twin-turbo GT2835 or the single turbo HKS TO4Z? I know the twin-turbo takes longer to deliver the power due to its lag and slow spool up, but how do they compare in overall acceleration and power?

They're quite similar - the biggest differences are in price and reliability. A twin-turbo header is much more expensive, and a twin-turbo setup has twice as many failure points. The only reason Toyota went with an oem twin turbo setup is because the oem twins are sequential. The parallel GT2835s are parallel and have no significant advantage over a similarly-sized single turbo.

Am i correct in my instinct in going with an HKS turbo system, or is there a better option out there? Also, should I go with a pre-configured system, or build my own through HKS?

For resale value and quality of fitment, HKS is top of the line. A very good choice, imo.
There are cheaper options, but often at the expense of quality/relaibility, kit-completeness, and/or fitment.