A hotel I have been to several times in Fuengirola is the Las Palmeras. It is a large hotel right behind the marina so it's very close to just about everything! The trian station is a couple of roads back where you'll be able to go from Fuengirola all the way to Malaga. There are plenty of restaurants, bars and shops around Las Palmeras whereas the other hotels mentioned are a bit further away from the main part.
My husband and I have been lucky the time we've stayed there because some people have been unlucky and ended up with a room overlooking the London Bar which is on the opposite corner to the hotel and can get very noisy but it shouldn't be too bad in October which is when we've been. We've also been in July and it's certainly a lot busier in Fuengirola then.
You mentioned Benalmadena but I don't know if you'll have heard that it is VERY hilly in places. If you wanted to go on the train the station is a long way up, although there are some further along on the outskirts of Benalmadena. I think I know where the Riviera hotel is and I've read that the gardens lead down to the beach but there are quite a few steps, although there's also a lift. If it's the hotel I'm thinking of the back of the hotel is very close to the beach but the front is on the main road which is busy and a lot higher than the beach.
If I had to choose which hotel I would definitely go for Las Palmeras rather than the Riviera, just because it's all on the flat and there's much more going on in the area.