If there is a downside to Marsa Alam, it would be the lack of nightlife. It is the total opposite of Sharm el Sheikh. Bear in mind that there are fewer divers, too.
Clearly some peoples downsides are other upsides. Sharm these days is rapidly turning into my version of hell. Too many divers on the popular sites and far too much noise pollution, but that is to digress. Some of the Marsa Alam hotels are now acquiring that delightful late night noise so beloved by those of us that want to get in an early morning (i.e. 06.00) dive for the low light. I was also in Shagra in June and it was the first time that I had heard it there but it is meant to now be a regular feature.
I have been to Shagra a couple of time and I have also just come back from the sister camp, Nakari. For me the choice of the two is Nakari. It is quieter, far more personal, and generally has a better ambiance. For me the diver was better. More swim throughs and decent shallow corals, large shoals of ghost mackeral (bigger than those at Shagra), bait fish, and wrasse. We also regular had large numbers of squid. Dolphins are also meant to be more commonly seen in the bay.
If you want clubs and pubs then stick to Hurghada and Sharm. If you are not with an all photo group then there is a good chance that they will want you to follow the herd. If you want unrestricted easy diving shorebased then I would go for Marsa and the Eco Villages.
I am going to the Marsa Shagra camp in April. Those of you that have been there, on the house reef, how much control do RSDS apply to get people to follow buddy rules? I have the SDI solo certification, and will dive with a pony.
Regards Bent
You won't be allowed to solo. Although it has been known to person to add their name to a group, go in with them and come out at about the same time 
Daniel