I would recommend an ACE 250 or 350 without hesitation.
I had my ACE 250 since about 2004 and was quite happy until my wife and grand kids got interested in the hobby and started cutting into "my" swing time. That was enough justification for a second detector so I chose the AT-Pro. It was an excellent move and keeping the ACE is a nice second detector for another person wanting to join in the hunt. The ACE also sits (quite often) in the trunk of the car with the sniper coil on it and still gets used by me for the real trashy areas.
But... hey "lucky steve",,,, you better get a digging tool for your fiancee if you want to get out of the digging. Take it from me, having the second detector only solves part of the problem. I find that everyone loves detecting but the excitement really dwindles when they realize they actually might have to dig for themselves. LOL