Sliema is a great place to visit this time of year, with shops at your door step, beaches, bars and restaurants at every corner. If your looking for Soul with some sunshine, Malta is one of the better odds you can get.
We went to Malta last year in June and it is crazy expensive out there, the Euro messed it all up. Taxi's cost a fortune so would deffo hire a car. We went to Mellieha Bay, and there wasn't much going on in Summer so now Id guess it would be like a ghost town. The Popeye place will deffo be closed I would've thought. So your best bet would be to aim for the capital (Valleta region) or Buggiba town, we drove through here and wished we'd stayed there, looked a lot busier.
Canaries are what they are... and costs a fortune to fly there annoyingly. Lanzarote will be the coldest as it gets all the wind. Teneriffe is your best bet.
Will it still be warm enough to swim during the day? We went to the Lake District this summer and I'm really craving some sun before winter kicks in with a vengeance. Also, we don't want to have to hire a car. Another option seems to be the Canary Islands but they're quite pricey and it seems a bit soulless.