I don't know your climate, so I couldn't say when is the best time, but my packages get here in April, and I'm sure it colder here.
As far as nucs or packages, if you can get a nuc on the size frame and the kind of comb (small cell, natural or whatever) that you want, and you can get the nuc from a reputable dealer, I'd get the nuc. If not, I'd get the package...