I'll echo the praises for RIFT's weekenders. I went to Shift Your RIFTs this year for the first time and was super impressed by it. It was well run with plenty of staff to make sure things went smoothly and there wasn't too much cheating; I encountered a single person across the entire weekend who wasn't taking his hits. I haven't been to the epic weekender that they have coming up, but me and my friends may be heading there as we have no interest in the NAF now and it is probably a good alternative.
Outside of that, I go to AI500 regularly, but that's more of a social thing. The airsoft is usually generally poor, though I'd argue it's a bit better than the NAF, but the sites they secure are usually really great. I also go to Gunman's filmsim weekends, specifically Vietnam for myself but they also do Cold War, 90s and even Star Wars events! They're well run and a good laugh, run by a good team of people, though they have a few kit requirements to make sure everyone looks the part. Can't turn up to a Vietnam game in multicam with a hi-capa running m4 mags, but at the same time the kit doesn't need to be totally 100% accurate, no matter what the stitch-counters may say. An m4 with plastic grips and a carry handle, paired with a simple pair of black pyjamas and a chicom is a perfectly adequate VC kit, for example (captured weapon)