I've been to London in 2014 and 2012, both times stayed near Paddington Station/Hyde Park neighborhood. Easy walk from train station, tube stations nearby, restaurants and pubs all close. Reasonably priced hotels but be careful, check to make sure your room is "en suite", meaning it has a bathroom, otherwise you will be sharing with other guests or using one down the hall. Not all hotels in Europe have in room bathrooms (not like here). Also make sure the hotel has an elevator(lift), otherwise you may end up walking up several flights of stairs to your room(like I did last year). The Sussex Gardens neighborhood is very nice and relatively quite, just a five minute walk from the Paddington station. Hotels get more expensive the closer to central London you go. You mentioned the Victoria/Belgravia neighborhood, a good choice, on the south side of Hyde Park, very close to Buckingham Palace and Westminster Abbey, but more expensive, hotels on the north side of Hyde Park a little less expensive and the neighborhood is quiter. Either location is fine, just depends on how much you want to spend for a hotel. Taxis are very expensive, try to avoid them, you can get a visitor Oyster Card by ordering it online, it comes to your home pre-loaded with $$$ that you specify, that way you just swipe it when you enter a tube station and can go anywhere you like in the London area. It takes 2-3 weeks to get it so order it soon if you are going in May. Just google "Oyster card". They also work on buses, another fun way to get around the city. Enjoy your trip, bring comfortable walking shoes.