not sure I agree. Patong is horrible, but there are some nicer places in Phuket. The beaches and scenery are much nicer in Phuket. Not saying I love the place, but I would choose Phuket over Pattaya.
Depends what you want to see. If nice beaches are your thing then definitely Phuket (I would avoid Patong).
If it is temples and street food etc then Bkk is a better choice. You could catch the bus to Hua Hin to make it a two centre holiday, it's about 3 hours away.
also, don't forget you need a medical certificate from a doctor and a letter of residency from immigration too. Both easy to get for a couple of hundred baht.