Coptas IMO are a waste of points and are one of the worst ork pieces in the Codex...dont feel bad though i have a ton of them as well from the AOBR set.
Coptas are one of the most powerful units orks have until you get to about 2k points, youve got a S4 on the charge, 3 attacks, 5T 2W and 4+armor that can outflank and moves 18 inches a turn if you assault, FOR ONLY 35 POINTS. with the option of powerclaws, yeh theyre only S7 on the charge, but thats enough to rip open most vehicles and annihilate nearly any other unit. Someone at my game store runs 9-15 usually and theyre brutal as can be, he usualy runs 1-2 powerclaws in a squad depending on points, outflanks them all and then lines them up so he can dual assault vehicles with powerclaws, and weaker units with the normal boyz. it makes it a lot harder to play against them, you have to stay away from the edges cause very few units can stand up to being charged by deffcoptas, it takes a melee heavy army, like chaos or marines to not take some serious damage from them. I watched a game a friend of mine played against him,
IG vs Orks with 15 koptas. 2nd turn a 5 man kopta squad flew in and in one round of melee destroyed a leman russ and sweeping advanced a 20 man guardsman squad, not losing a single kopta.
keep in mind that most armies have S3 as the common troops S,
IG, eldar, dark eldar, tau, about half nid armies, excluding stealer swarms, non khorne chaos deamons, orks(as long as you charge them, which is the point of a jetbike outflanking). that makes most enemies take a 6 to wound them, and most of the rest of the armys' base units are 4S, so still a 5+
theyre insane if you use them right