In the teardown video of the MDO3000 (recorded a couple years ago) Dave mentions that he will be doing a review, but I can't find it. I found the one for the Keysight MSOX3000T but not this one. I'm trying to decide which of the two to purchase.
Well, I have a Tek MDO3054 here, and I wouldn't recommend it to anyone. It's slow, and I mean really slow, the built-in "SA" is a joke, and the UI comes straight from hell.
If I had to chose between the MDO3000 and a MSOX3000T I'd take the Keysight hands down, because it's the much better scope than the Tek. It's disadvantage is that it comes with tiny 4Mpts of sample memory (which depending on what you do can half or quarter), and it's really very expensive.
Any reason your choice is just between Keysight and Tektronix? As mentioned there's also R&S (the former Hameg HMOs as well as R&S' own RTM Series), and last but not least LeCroy, who has the WaveSurfer 3000 which is a lot cheaper than the MSOX3000T but still comes with various advantages over the MSOX3000T.
However, it very much depends on what you want to do with the scope, which decides what features could be useful to you.