I'd recommend sticking with APC....I've explored other UPS vendors/brand in
the past, and most of them work fine especially optiups....but I've also
had some cases of cheaper ups's becoming fire hazards, having short useful
lifetimes, or not producing a good enough sine wave.   When power is subtly
wrong it can also be exceedingly difficult to troubleshoot, and I'd rather
not go through that again.  There is also a larger community to
troubleshoot issues or to get replacement batteries with APC than with
other vendors.

So, given that, it mostly comes down to choosing which APC ups to go with-

BackUPS is OK, they are great value, but the quality seems to vary by year,
replacement batteries may fail early, and you need to verify the sinewave
specs.
SmartUPS SMT-1500 is mostly what I use now as it is more durable, displays
more info, has expansion capabilities, and seems to handle most power
events better.

For Gentoo, you can monitor the UPS's with apcupsd package.  Note that some
models are not fully compatible w/o buying an SNMP mgmt card...but the
critical stuff works fine.

You can go with cyberpower and other mainstream low-cost vendors, of course
- it depends on how much you value what you are connecting to it.