They're very different, but I like the Gazelle for a comfortable and fast commute (about 10 miles on the West Side Greenway each way). Being able to go 28mph effortlessly or get 50-60 miles of range is really nice and welcome flexibility. And it has the power to make towing the Burley with my kids in it really easy even in Eco mode -- we went about 20 miles into Westchester (40 round trip) on the South county trail last week and it made it there and back with about 10 more miles of range left. That long a distance with the trailer would have killed me on my old mountain bike
But the Gocycle is great too, and much more flexible in different ways that are probably predictable. Like when I know I'm going out after work, I can fold it and bring it inside with me instead of worrying about it being locked outside. I've brought it to several restaurants and bars and it's small enough when folded to not get in anybody's way it raider questions. Range is lower and it doesn't have as much power, but 20mph is plenty in most areas and I tend to stay in Eco mode on both of them anyway so that I'm getting at least some workout, and that gives me 35ish miles on the Gocycle, which is plenty in most scenarios. The Gocycle is still a bit more of a novelty and turns more heads
It's nice to bring into our apartment to store instead of in our building's bike room where the Gazelle is probably safe but I still lock it with the cafe lock just in case.
I think it really boils down to the Gocycle legitimately being easy to fold and stow in a car trunk, carry up steps to bring with me somewhere, and being a super flexible urban bike. The Gazelle is a really well rounded bike for getting around when I know where I'm going and am comfortable with where it's going to be parked. It's hard to understate the flexibility of the Gocycle though because you really can bring it anywhere and the fold is so easy. I've only had it about a month though so can't speak to reliability - both have been great so far. I do ride the Gazelle more often though because my commute is very predictable with a bike room at work and also at home, so I charge the battery inside overnight and ride it in the morning.
The Gocycle being so "connected" is both good and bad. The app to control the bike is very flexible, and had a really nice configurable dashboard. But it can also be confusing and I don't love the activation of the bike being tied to an app and your email - if the company goes under, which to be fair send unlikely especially given the popularity of the GX, the bike will suddenly become much less flexible and basically be stuck with whatever settings you last updated them to.
Sorry, a bit long winded, but hopefully that's useful!