I own both, although have only had the TT a few weeks. They are both fantastic and I plan to shoot matches with the TT this year to see if the ZCO becomes a TT or the TT becomes a ZCO.
So far, I kind of like the ZCO more. It has much more elevation adjustment and can focus down to 25m, so its a much better option for rimfire games. The Gen3XR is a nice reticle but its a bit on the thinners side. The MPCT3X is about perfect and the dots really do help you make faster adjustment on the clock. The turrets on the TT are hard to beat and rezeroing does not get any easier. Glass wise its kind of a wash, the TT does look cooler and more natural where the ZCO seems a bit brighter and maybe more pop. I haven't shot the TT in mirage yet but I assume it will equal or exceed the ZCO. Both have locking diopters which is nice. ZCO gives range estimates on parallax while the TT doesn't if that matters.
I got a really good deal on my TT and it was cheaper than a new ZCO. I would NOT pay $5K for one based on what I have seen so far.
You really can't go wrong with either unless you need the features for shooting rimfire, then the ZCO is an easy choice. I think it comes down to reticle, turrets and if you need more elevation.
If I had a gun to my head and had to pick one, it would probably be ZCO. I think its a peer at a much lower price. Each one has some things it does
better/different than the other but the reality is, you are choosing between a Lambo and a Ferrari. Neither choice will disappoint you.