Haven't been to Pattaya, so this isn't responsive to your question comparing the two. Also, I'm reporting after visiting the area as a couple, not as a single. The two approaches to exploring Thailand couldn't be more different. So, for what it's worth...

In Phuket, there are many areas and beaches, the principal one being Patong. Patong is a central town for the district and there is a lively downtown and a beach which is less sumptuous, but more um uh "popular" than those farther away.

We stayed at a delightful hotel called "Tropical Resort" on Kata beach, after being shifted from the Tripadvisor-celebrated place we had booked. I was very sceptical at the sideways shift, but it turned out that the hotel company had just built a palace, had no guests there and wanted to populate it, so they overbooked their 2.5 star and pumped the overflow into the 4-star, no extra charge. Possibly the most dramatic free upgrade I've experienced in my travel career.

Anyway, the beaches: Kata is odd but nice. Odd, because back in the day, Club Med bought all the land fronting it, so the only public access is at the very end of it. The beach is public. Sadly, it suffers from a common problem: there is a moment, early in the day, when all the vacant beach chairs are suddenly claimed by invading hordes from the resorts. How they coordinate this I've never underestood. But you can look at the beach at 8am, see it empty, return an hour later and find no vacant chairs. Without an umbrella you are doomed to a short visit or a day in the water. The water is exquisite.

Kata beach has so-so, unremarkable food options, unless you walk up the back road and buy grilled offerings from the street carts (great) or Tom Kha Gai (splendid) from the little family-run restaurant farther up, where the tables are served by the trans girl while the mother works in the kitchen. Food great and criminally cheap.

Bus to Patong is fun and makes a good day outing. (Not that kind of outing!)

If I were doing it again, I'd stay in Kata or somewhere like it for the beach, hunt and eat in Patong.