Ive stayed in the Bellevue but not the Alcudia Pins, although I have been in the complex many times.
In my opinion I would choose the Alcudia Pins. The bus along the road is every 10 minutes and very cheap. You will be right on the beach, although you are a bit out of the centre, you can get in very cheaply.
The Bellevue is very central, however (my experience only..........not casting aspersions on anyone who enjoyed the place)............I really didnt like it at all, the block I was in was very dingy.
If it was me I would stick with the Alucida Pins, but thats just me!!!!
Im sure you will have a wonderful holiday anyway!