I agree with Detector ,a Etrac or a v3i..The Etrac is pretty straight forward,and does a great job at going deep and the Id is solid..I'm also a big fan of the At pro.So,when I get to running a Etrac it's all good at first.Then it starts,I wanna go like I do with the at pro.And you just can't,you gotta go slower with the Etrac.If not you'll miss stuff...But the Etrac is just a great deep machine.
The v3i I've never owned,always wanted one though.The only thing that has stopped me is the hype of how involved it is to setup.Ive actually lost sleep over reading about that machine.If you watch videos of that v3i it has a high definition color screen ,just the best I've ever seen.And it can be tweaked a million different ways,but has a ton of presets.
If I were in your shoes,which I kinda am,,I would get a nice used v3i which I will this year..Since you have the At pro ,if the v3i gets you frustrated you can run the Garrett,then cool down and go back to the v3i...From what I see it's a machine you'll not grow out of,period.Look it up on YouTube.