I have both the Trektop NX and now the OEM soft top I purchased off Craigslist.
I also prefer the fastback look to the standard box top. Other than the appearance, here are the notable differences between the two styles (applicable for Unlimited version only).
1. Opening the top. The sunrider feature of the Trektop basically allows it to fold back over the rear seats. So when open, the front seats are completely open but the rear seats remain covered. This really has never been a concern or issue for me.
2. Front and rear arch supports. The Trektop has arch bars over the driver seats, so when you open the top, unless you also remove the arch bar, you have a bar still over your head. This really has never been a concern or issue for me.
3. Thump and bump. When running the Trektop with the rear/side windows out and the doors off, I had a MAJOR clunking sound that really concerned me. It sounded and felt like it was coming from the underside of the chassis. I spent a good bit of time yanking on parts underneath to find what was loose. I was about to take it to the dealer when the lightbulb went off and I realized that it was only when I had the top open and doors off. I determined it was the sunrider frame banging. I bought some velcro straps and solved the problem. Just a heads up if you experience this.
4. Fully opening the Jeep. Like the OEM soft top, the Trektop requires you to remove the rear and side windows if you want to fully open up the rear cargo area. Because of the design, there are hard plastic supports built into the side windows (this is how this top works without a frame. Basically, the frame is integrated into the windows by way of this rigid plastic). This makes it almost impossible to roll the windows up in any way to store in the Jeep while you're out and about. Also, noting point 2, unless you physically remove the entire top, the rear seats are still covered bikini style. So what I've done is removed the rear and side windows and left them at the house when I go out. This makes weather watching VERY important. It also robs you of a lot of the flexibility inherent in a convertible. With the OEM style, you can roll up and protect the windows. Carry them with you, and fold the top entirely open. If a storm pops up, you have everything you need to put your top back up. This was THE reason that I purchased an OEM top after having used the trektop all summer. It becomes a big deal for out of town or long trips if you want the flexibility of having the top open.
Overall, both tops are great and I really love the fastback look but there is a trade-off.
I haven't had any leaks with either top.
Figured it was worth sharing since I have real experience with both tops.