Hi!
I think a night or two in Kuta after 3 or 4 nights in Ubud. The time in Ubud for relaxation and enjoyment, the time in Kuta so that you know what you haven't missed by being in Ubud
Perhaps that is unfair, so maybe do Kuta first so as not to spoil the end of your stay in Bali.
There are other places in Bali really worthwile staying such as Pemuteran, Amed etc. but for a first visit I would say Ubud.
If you want coastal and near some action maybe consider Seminyak.
All IMHO
Regards,
David