What's to compare? One is a 2-channel pre-amp interface that offers nothing outside of in-camera audio recording. The other offers better metering, better controls, 4 independent record tracks, and recording to SD card so that you aren't stuck with DSLR in-cam (lesser quality) sound recording. The DR-60DmkII might be a more logical comparison simoly because it is also 2-channel, but even that's a stretch.
These are two very different devices for very different practical purposes. Either way, I don't recommend relying solely on in-cam DSLR audio recording as it still isn't up to par with external recorders. The DR-60DmkII and the DR-70D offer outputs to feed the camera, so you have the in-cam and external recordings and can make easier work of sync in post.
Well they are kind of apples and oranges. One is a four track recorder with mic pre's and the other is a two track mic pre that has no recording capabilities.
The DXA-SLR ULTRA is $90 more than the Tascam DR-70D - so from a financial point of view the DR-70D is a better deal.
But beyond comparing specs on a sheet and claims from the manufacturers, it can also be a good idea to read user reviews for real world feedback. Here are some user reviews from B&H: