While I don't hold myself out as an expert in rack mounted UPS systems, I can safely say that APC is pretty bad after tossing a bunch of them out shortly after they're purchased.
I have found the folks at Don Rowe helpful for power inverter stuff. In my case for marine applications. I really like the KISAE inverters / UPS - have three of them that have been running for over a year in some fairly tough conditions.
But there has to be a better professional vendor than APC. Even their mid range stuff is put together like typical Chinese consumer electronics. The KISAE units are much better finished and have beefier PCB boards, mountings and hardware.