I waited until 60 for these reasons:

Everyone I know who went at 58 couldn't hit 62 before Zangarmarsh (prereq level for some quests)
There are plenty of non-collection 60-ish quests in Azeroth
There are plenty of 60 instances (need to level cooking? Go hang out in DM)
Nobody hangs out in Azeroth anymore - no worries of gankage (which is TYPICAL in hellfire peninsula on my server)
Hellfire Ramparts is ROUGH even with hellfire gear at 61-62. (I'm thinking Nazan here). If you run out of quests before Zangarmarsh, you'd either have to suck it up and farm Ramps, or see if you can do BF depending on your level/gear.