Either ,but,my preference would be a lurcher,of medium size,that the parents do the work you want the pup to do ,see as many litters as possible,ask many questions ,be a pain in the arse ,if they don't want to answer,walk away.
I'd be wary when they own both parents and they are both young.
Oh and do a search on here as it's been asked loads of times and the usual answer is collie x greyhound x whippet or something similar,
But get something that you like,beware of puppy pedlars