Edit: Based off some comments, I've included options for non-lovers of meat. Also added other comments.
For a lot of user groups, food depends highly on the sponsor for the month.
Let's keep this short and sweet: Sponsors. If your instinct is to order pizza for a user group meeting, your attendees already hate you.
Think about it this way. A lot of people have an opportunity to sponsor a group. You want to be memorable. Pizza is not memorable.
And you know what else? Sandwiches. This is the new pizza. If you think you're being clever and different by providing Jimmy Johns instead of pizza, your attendees hate you too.
What could you do instead of pizza? What food would make your company memorable? Here are some ideas:
Chipotle - When I spoke at Richmond .NET in October 2015, MaconIT brought Chiptole burritos. I'm talking about a box of freakin burritos.
Taco Bar - Taco bars are fun, and they allow attendees to choose their own mexican adventure.
Chick-Fil-A - Nugget tray. Enough said.
PF Changs - How about some asian flair? Try a mini-buffet of PF Changs favorites.
BBQ Buffet - Pulled pork, beans, coleslaw. Depending on the location, you can get a BBQ buffet for the same price as pizza for a group.
Veggie/Vegan Options - I know, I know. The food above is all mostly of the animal protein category. Please don't forget people that don't eat meat. Salad choices and veggies go a long way. You'd be really surprised how many card-carrying meat eaters will dive into healthy choices. Not sure what Vegan's would eat? Ask one. They'd be more than happy to give you a couple dozen options.
Don't get me wrong, pizza is awesome. Pizza in EXCESS is horrible (and to be fair, if you brought Chick-Fil-A every meeting -- that would probably get old too). Be good to your groups and don't buy pizza (or sandwiches). Look for creative alternatives. Attendees will love you.