Originally Posted by
stapfam
Hate to say it but the better quality RD I get- The longer they work efficiently.
For a 34 you will need a long cage derailler. Acera- Deore- LX- XT or XTR. All will work fine but The lowest I recommend to use is LX. Problem with Deore and lower is that they do not last long before the Bushings and Pins get a bit of wear in them and they go sloppy. For me that is less than a year but LX and I can get about 18months or 3,000 miles on the MTB. For that reason I always use XT which may be over the top for your use.
In hard, rough and dirty mountain bike riding, yes. But with light duty on a road bike, keeping it clean and lubed etc., a lower end MTB derailleur should work just fine for many years.