The choice is really between the shelf ones and the basket/drawer ones. I have ended up with one of each, as I have a shelf one in the caravan and a bucket (Ninja) one at home. They are different beasts.
The shelf one is like a mini oven. Tonight I have cooked a leek and potato pie and a Countess pudding in it (for an inadvertently 1940s style meal
) and they cooked exactly as they would in the big oven, but in less time using less power. I assembled the pie first on a pie plate, and cooked the pudding in the fryer from the raw batter stage in a pudding basin. They are great for Yorkshire puddings too.
The bucket ones would struggle with that sort of thing, as you can't easily put dishes in them. If you find one that fits you struggle to get them in and out without spilling the food and burning yourself. Where the bucket ones come into their own, however, is for things like chips, or anything that you might want to deep fry. They have a larger capacity (or the large ones do) and you can shake the food easily to get a more even cook. The shelf ones have to have the shelves turned and rotated otherwise the top one cooks faster than the lower ones.
Both cook chickens better than in the oven. I would say that if you want to make scones etc the shelf one would be a better buy. Mine is a Tower one, too, and I'm happy with it. I don't know that either of them would replace an oven, but I use mine much less often now.