Hi guys, I own a 2012 Felt Nine Sport and am looking to upgrade my shifters. They don't shift as quickly as I would like.

The bike comes stock with:
9 speed Acera shifters


Shifters:
Shimano SL-M390 9 speed Rapid Fire
Front Derailleur:
Shimano FD-M430: top swing
Rear Derailleur:
Shimano Deore FD-M592 Shadow, long cage 9 Speed



What would be a compatible shifter I could upgrade to?

Thank you,
Carlos

If you mean the shift takes some time after you shift the shift lever, that's not the shift lever's issue. Your best bet would be to check your RD alignment, replace shift cables & housings, and adjust the derailleurs. Also, the rear downshifts occur at the shift ramps on the cassette cogs, so they're still the final bottleneck. You have to wait for them to come around.

If the issue is that the shift doesn't occur until you pull AND RELEASE the upshift lever, then you could get XTR M970 shift pods, which not only feature instant release, but can upshift two cogs in one shot if you pull the upshift lever past the first detent. Nice shifters (but not cheap).

Acera is 9-speed now? When did that happen?

Pretty much any 9-speed Shimano shifters should be compatible. I think mechBgon is probably right that the shifters aren't causing the slow shifting, but if you just want to upgrade I think the M590 Deore shifters are a great value.

To echo what's been said above, your need to adjust your derailleurs. Best shifters in the world will shift like crap if the derailleur isn't adjusted properly. A more expensive derailleur will need adjusting less often. So your first order of business is to read mechBgon's post again. If you still want to upgrade after that, I'd suggest going Deore.

Thanks guys! I dropped off the bike yesterday for my free tune-up at the LBS.
If it's still iffy after the tune-up I'll save up for upgrades.

Just upgrading the shifters probably won't give any increace in the feel / speed on the shifting, for this you will need to look at upgrading the deraillers and possibly the cables as well.

Being as you currently have a 2012 bike, you would need to look at a substantial upgrade to XT or XTR to get a noticeable difference, but any upgrade will have this added issue of needing to look at going 10 speed. Alivio / Acera are the lowest groupsets still on 9 speed, with everything else above being 10 speed.

Would follow MechBgon's advice on setup, and save your money for a new bike in a few years with better components when you have worn this one out.

XTR SL-M970 the best shifter for 9 speed