Either would do, but the Tripp Lite already has a USB interface. The APC SU1400NET doesn't (RS232 port only). In the past, the USB to RS232 cables didn't work under OS X, so users had to find a PCIe based Serial card that will work under OS X.
As it's just a download, I'd expect that APC will help you out if it doesn't already contain the newer firmware. Their enterprise support is quite good.
It's probably a Line Interactive (4ms is fine), but we'd need the exact model number to be sure (BTW, I suspect it's a re-branded CyberPower unit).
Yes, it's a Line Interactive unit (AVR = uses a multi-tapped transformer to pick up or lower the wall voltage to an acceptable level when not on battery).
They're both Online units, so the Tripp Lite is cheaper initially. But what you have to keep in mind, is that the batteries for the Tripp Lite are more expensive.
Yes, but you can still get a refurbished pure sine wave unit for the same money, perhaps a bit less (personally, I'd wait for a longer track record from the CyberPower unit - more time = more users reporting their experiences with it, particularly longer term). And between the two types, a pure sine wave is a better unit to have (will not cause problems with PFC based power supplies, have a long track record = known to work, and continue to do so even after the warranty period has expired).
