It's all personal preference
I got the power rack. Mainly cuz my wife drives the car occasionally, though since the new motor went in she's afraid of it.
Ask yourself how you are going to drive it.
I once watched an interview with a F1 driver, Arie Lyundyke I think. He said that he never used powersteering in his race cars. His theory was that the other guys that were used to power steering would not be able to finish a race if the PS pump went out, and he'd have and edge over them.
If your building a track car this may be something to consider.
You have to love the simplicity and lack of crap hanging off the front of the engine with manual steering.
If your young, have a limited budget and can hack it go manual. Put the money in HP or traction.
As for Me, I'm old and my wife has my nutz in her purse so I got PS and AC.