The two pistols are very different in many ways and are an apples and oranges comparison in some ways. The overall sizes are similar, the m&p being a little slimmer though. Trigger pulls are very different. Accuracy is better with the Beretta in most examples, but these are combat type guns, not target guns. The m&p is "easier" to operate since all you have to do is pull the trigger. The full size m&p holds two extra rounds (when limited to factory mags), but that really is kind of negligible anyway. Both guns have a very different feel to them, a personal preference issue. The Beretta, whether hated or loved is extremely reliable. It will not be hard to find negative critique about it. But some of the stories (if true) likely originate from conditions one you would own would never be subjected to. Also, the Beretta actually had to meet some standards many pistols might not meet when it was adopted.
Just get one of each.
