I went to Ponto do Ouro last year for a weekend when I was doing volunteer work at Tembe elephant reserve in SA.
It definitely has what you're after in terms of beaches and diving. However, it's a pig to get to unless you have your own 4X4 transport. It's very isolated and you need 4X4 for the roads in either direction- to Maputo is a long haul on sand roads and to the SA border is a short drive but also on sand roads. Coming from SA, if you have a non 4X4 you can leave your vehicle at the border and some accommodation will pick you up. From Maputo your only real option is to pay for a transfer with your accommodation- unless you are lucky enough to be able to hitch a lift.
There are quite a few South African tourists there, and because it's so isolated from the rest of Moz, in some ways it's a bit like an extension of South Africa. Most places accept Rand, and when I dived, they only did the briefing in English for my benefit- if I hadn't been there it would have been in Afrikaans.
Tofo would be logistically an easier option for sure although I've never been so I can't compare the beaches or diving.