These days I pay the 30% or so and go for "double conversion" or "online" UPS's. They have two invertors. One charges the battery. The second takes the battery and powers the gear. Your gear is always running off the battery, there is never any worry about transfer speed. And since your equipment is never running off the mains, AVR just happens as a byproduct of this design.
B.E.S.T. used to make the best UPS's (pardon the pun) but APC bought them a while back. A few of the APC models used to be easily descernable B.E.S.T. designs, but these days I can't tell if any of their current ones are previous B.E.S.T. designs. And since APC has been coasting on their name for some time now I no longer recommend them. Liebert is a great brand and if you can afford them you could do allot worse. I have a hard time justifying brands like Liebert and luckily I've had really good luck with CyberPower, a brand that seems to be in the Behringer sweet spot of features and price.
The problem with UPS's, even with AVR, is if the power gets too bad you will switch to battery. I've seen online UPS's hang on where AVR UPS's would drop to battery, then run out of juice and finally die. The online wasn't getting enough to keep up with the battery, but what it could suck from the crappy mains power keept it alive until the gig was over. I hate extension cords...