I really like my Horipad Ultimate. Haven't used the Nimbus, but 9to5mac.com said they preferred the Horipad. It's apparently a little heavier than the Nimbus, and they said it felt better in their hands. I've heard the Nimbus has a slight delay on Zen Pinball, but the Horipad definitely does not. Oh, and the Horipad battery lasts twice as long as the Nimbus.
I purchased a couple Nimbus controllers with my Apple TV. To me they are flawless. I have not experienced any delays and feel perfect. The fact that it charges via a lightning cable is a plus. I now use one for my iPad and has made many games more enjoyable; specifically Wayward Souls.
I have used both. While they are both very good, I'd give a slight edge to the Horipad. The ergonomics, d-pad and buttons felt a bit better to me. For the record I own a Nimbus.
I've got the c.t.r.l.i, only because I've had it for aaaages. With the exception of the d-pad Ive no other issues with it. Though I am tempted by the Nimbus because of the cross d-pad.
I have a nimbus and really like it. It's just as comfortable as a modern controller. Probably get another in the future after we get a few more good multiplayer games.
As an owner of both the Nimbus and the Horipad ultimate, I give the edge to the Horipad, and I'd honestly be a little bit surprised if anyone who has used both would disagree. It just feels a little sturdier, a little higher quality, a little more durable, and a little smoother. The analog sticks on the Horipad feel almost exactly like PS4 analog sticks. Very smooth, very solid response, very sensitive. The sticks on the Nimbus feel stiffer, and all the buttons on the Nimbus (especially the triggers and shoulder buttons) have this feel to them as though they're being supported by a cheap spring that could wear down over time, almost like how an N64's analog stick would become loose and wobbly over time. They're both very good, and if I broke my Horipad or something I'd have no real qualms about using my Nimbus instead, but given the choice of the two, I reach for the Horipad every time. It feels like a true premium controller that could hold up very well when compared to the PS4 or Xbox One's controllers, whereas in my opinion the Nimbus feels a noticeable step down in quality over current-gen console controllers. It's still a better controller than Steelseries' last controller, the Stratus, but the Nimbus still has a little of that lighter, plasticky feel to it that just feels a shade under "premium". It feels like back in the day where you'd go to a friend's house to play Super Nintendo and they would pass you a Mad Catz Super Nintendo controller. The controller would work well enough, it just wouldn't quite feel the same as a 1st-party controller. The Horipad feels like a true premium controller in my opinion. And with double the battery power of the Nimbus at a similar cost, if you haven't yet bought one or the other, you have one very confident vote for the Horipad.
Thanks for that review Quazonk... will pick one up this weekend. I have the mad catz, which I'm perfectly happy with (it was the first one I think to break the $50 barrier). But I love the idea of lightning recharging, and I have to say, the Horipad looks pretty slick. Edit 2/26/16 Loving the horipad. Quazonk's write up is pretty spot on. Charge lasts forever, lightning charge in any of my iPhone/iPad chargers lying around, sticks feel great, feels great in my hands, Bluetooth connects instantaneously and I notice no delays while playing. I didn't know how bad the mad catz was until I tried this (truthfully the mad catz is not all that bad, this is just so much better). Buttons have the slightest of delay, meaning you start to push and feel a tiny movement before it engages. If you do a lot of platformers you notice it. Not enough to be a deal breaker at all. Also the LR lower triggers are a bit mushy. The only thing I've used them on so far is the dune buggy racing game for acceleration, so it didn't bother me at all. That's the only thing I can nitpick, this is a great controller, I'd recommend to anyone.