Those are both decent choices, and here's my comment. They both seem to be carbine length gas systems with a 16" barrel. Midlength gas systems are getting more popular as they're easier on the bolt carrier group, and midlength is perceived to have a softer press. If I had either of those blasters my first change would be to swap out the barrel/handguard for something else (or build a new upper) , but I think they're both fine to start with.