For case fans, S-Flexes on a fan controller would be ideal. GT's might give better performance/noise but as a case fan, I never found them spectacular (different story when factoring in static pressure). Yates would be a good option as they are really nice fans for your $$.
I've always been a fan of controlling...fans...from one centralized location (i.e. front bay device). I can't stand having to open my case to change something like that.
If you really want to stick with the same concept, email antec support and they may send you replacement fans. There aren't any better fans that use the same concept.
Some fans like Silverstone can come with PCI slot control if you want to go in that direction.
Otherwise there are many recommendations throughout the forum on case fans. I'd recommend the Scythe Gentle Typhoon for around ~$15, the Scythe S-Flex for ~$10, and the Yate Loon d12sl-12/d12sm-12 is about the best $5 fan you can get.
a gt as a case fan is such a waste.. :\
All that performance in static without anything to hold it back...
Can be useful in situations where...
1. intake is blocked by hard drives or
2. exhaust has to push through a stamped grill
you wont be amazed in this type of scenario over a yate.
Those fans really need to be on sinks and radiators for it to merit the cost.
Lame, they're usually better than that. Bought more than 3 years ago? If not, it should be covered under warranty.