My usual disclaimer: I'm still relatively a newbie to longer range and reloading.
I think I'd go 3-18. Been using a 3-15 swfa and 5-25 xtr ii as the only comparable. So far, I have never shot past 600 just at a retail shooting range and I didn't exactly think the 15 wasn't "enough" magnification. And personally, I think there is a difference between 3x and 4x where 3x is much easier to open both eyes and scan the larger field view.