Either bow is going to be an upgrade from what you are shooting. I upgraded from a charger to a Nitrum last year but went with a longer ATA and got the 34.
This year, I got a carbon defiant 34. Haven't shot it enough to judge any major differences yet.
I wouldn't buy a used bow either...
I'd never know if anything bad ever happened to it...
What would be considered bad? Dropped or dry fired?? The only difference between the two I can see is one riser is carbon one is aluminum. The nitrum has the zero torque the carbon spyder does not. Does it make that much difference? New the carbon spyder was a lot more money then the nitrum though.
I wouldnt be weary of buying a gently used bow if i was buying it from either a reputable dealer or someone i trusted. I bought a year old hoyt flagship bow back in 09 at the height of the recession and made out like a bandit. Shot a buck with it every year except 2 and got bucks in rifle season those years. I would try to steer you away from 30" bows though if you have no experience with them. I made a mistake and bought a closeout hoyt faktor last year. Shot great at the shop 20 yard indoor range. Saved quite a few bucks on it but i just couldnt get used to it or get it dialed in the way i want my bows past 30 yards. I ended up trading it in a few weeks before bow season for a new carbon spyder 34 zt. I love the longer ata.
Cork90- not much difference in draw cycle or performance in the two. Some weight difference. Both will tune best with QAD rests. If you really want to stay in the shorter ATA bows, then look for a used Defiant. Yes, it's this years bow, but you can find them relatively easy. Dealers and shop pro's get them at a reduced cost, then sell them. Go to Archery talk. check the sellers positive posts. anyone with 100 or more positive feedbacks are pretty safe to deal with.
Those two bows are very similar. Both have Z5 cams both are 30 in AT both are hoyts with similar grips. Carbon is going to be a little lighter, nitrum will be slightly heavier. I would say even after shooting them side by side you may have a hard time deciding. A carbon bow will give you better resale.