For the 5.56 platform M&P, I prefer fixed power magnification over variable power scopes ... but this fits my purpose for the caliber. I use the Eotech XPS 3-0 with the G33 magnifier on my MP15TS. For the 7.62 platform M&P, I use the Vortex Viper PST first focal plane series scope in 6-24x50mm with MOA reticle with the Vortex Razor reflex scope for backup/close range.
When I talk to folks about scopes, I rarely hear anyone chime in on warranty and after-sales support. This is the first thing I look at when I purchase anything ... how a company treats you after they have taken your money. Companies like Leupold and Vortex are very committed to after-sales support ... and they also make great main-stream products that fit the budget and purpose of most users compared to specialty companies like Eotech and US Optics that focus on professionals. Semi-automatics are very rough on optics. If you are more than a hobbyist shooter, the probability that you will encounter an issue with your optic somewhere down the line is high. My experience with Vortex has been top notch ... and their no frills lifetime warranty is the real deal. When I had an issue with one of my scopes, I just dealt with a single individual (Stephanie) who was responsible for my claim from cradle to grave. Stephanie was easily accessed by phone or e-mail throughout the claim. When I had a concern with FedEx over the shipment of the scope (I thought they lost my scope), I e-mailed a note to Stephanie ... she called me on my cell phone not more than 5 minutes after I had sent the message, ready to help. I can tell you from my personal experience, you don't get treated like an old friend when you call Nikon or Bushnell for help.