Nice three-storey house (plus anothe level with a roof terrace and laundry room) near the point in Senglea. Perfect for us as we enjoyed the walks to the ferry and to Birgu (and beyond). The accommodation is fine and the communication with the owners is good.
The small park across the road is great and the view of the Grand Harbour is stunning.
We were there during the Senglea festival and the whole of the area was decorated. There were fireworks all during that week on an apparently random timetable.
Buses are available to the south of the island and the Tallinja App allows you to check times and routes.
Whilst you can swim off Senglea, the best place in the Grand Harbour is below Fort St Angelo in Birgu. The locals go there every afternoon and are always keen for a chat.
The ferry is linked to the Valletta to Sliema ferry by a free bus. You can buy through returns.
Senglea is quaint and appears to be at the very start of a gentrification process. So if you want to see the real Malta and meet with the locals you should probably go sooner rather than later!