I'm trying to decide which way to go 21inch tapered or 23inch bull.Tell me what you think.
The barrel will be in .223 on an older contender and will be used for varmit hunting.Thank you for your help and suggestions.
IMO the OP didn't give enough information to offer him a valid assessment. Only given is the choice between two standard Contender factory barrels. No shooting style or method was given (jump shooting offhand, using a handy "lean" spot and stalk, from a bench, a stand, etc).
"Varmint" doesn't say enough either as it doesn't give any idea of what the OP considers a varmint. To me there is a big difference between varmints and predators, the methods most often used and the ranges shot for each of them. Which adds that there is no mention of at what ranges most shots will be taken. Will he be shooting factory ammo or tuned handloads?
IOW, my choice for which barrel I'd consider the best would depend on all of the above factors. While either factory barrel could suffice good enough in a pinch in most situations maybe, one would be better than the other in some specific circumstances. I'm not really splitting hairs or over analyzing here... but in some scenarios the choice could make a difference between consistent success or failure.
All that aside (that most probably see as hogwash anyway), if I had to pick one of the OP's choices I'd opt for the 21" for general use (except for long range small varmints and predators). But a custom 20" bull with tuned handloads would be my first choice for every situation. Good balance and barrel harmonics, easy carry, easy to use in tight cover, etc; and the 223 will be capable of some impressive ranges in that barrel for very small targets.
FWIW-YMMV
L.