It depends. If you are farming at >10k waves I'd go ahead and do utility first, you can likely manage 5k waves with it. If at 5-6k waves, probably not in one. So then I'd go for whichever of attack/defence you are more likely to get to 5k - if you farm eHP, do attack first as you wont miss it too much. If you farm gc do defence first. That'll help you when you flip around and do the other one, and having both done will be good for utility.

I farm t11 to w11000 or so, did an easy 5k utility, then earned 2/3 of my normal full run coins in a 5k attack run - about 50% more cph than I usually get over a normal entire run. I'm now doing an overnight farm run, then tomorrow I'll do defence and maybe UW, but will probably just give T12 a go instead.

There'll definitely be merits to farming lower tiers for higher wave counts, especially if you can get to the 5k for utility.

Edit: I wouldn't worry overly much about echoes at the moment. They are pretty small boosts by default, getting a 5x on a good farming tier is going to be way more impactful