Issues like this are usually caused by the actual microswitch being faulty, so if that's the case then there's nothing you can do unless you are able to replace it. However, it's still worth trying to open it up to see if there's anything you can do about it. I don't have a Deathadder so I can't help you with that part, but I'm sure you could figure it out.
As far as getting a new mouse, I was recently in the market for a new gaming mouse so I can share my opinions on the Alienware TactX mouse and the Coolermaster Storm Sentinel Advance, which are the two mice I tried. The Sentinel Advance is very comfortable if you use a palm grip as I do, and the LCD is actually quite useful since you can set custom DPI levels and modify profiles on the mouse without having to mess around with software. The precision of the sensor is very good as well. The biggest downside for most people is that it uses the Phillips Twin-eye sensor, which has an issue that causes the cursor to jump down and to the left every time you pick up the mouse and put it down. I didn't find it to be much of a problem, but it really bothers some people so it's something to keep in mind. Another problem is that I find the mouse to be slightly unstable. Rapidly clicking the mouse buttons causes the cursor to jump around a bit depending on how firmly you're holding the mouse. This can get annoying, though having a flatter mousing surface helps.
The TactX is more designed for a claw grip, so it's not as comfortable for me. I am getting used to it though, and it doesn't really bother me after about a week and a half of using it. Although the Sentinel Advance tracks very well, I find the TactX to be noticeably better. It also glides more easily (I tried removing all of the weights from the Sentinel Advance to make it lighter than the TactX and then comparing them, but the TactX was still smoother). The build quality of the mouse is excellent and all of the buttons have just the right feel and the right amount of resistance, except for the mouse wheel. It uses the style Logitech first had back with the MX Revolution, which allows it to switch between a normal incremented wheel and a freewheel with no resistance. However, this gives the middle button a lot of resistance, and also makes the wheel rotate a little too easily when in normal mode (in my opinion). However, that's just another thing that takes time to get used to. A big problem with this mouse is that the driver software cannot be installed at the same time as Logitech Setpoint, so if you depend on Setpoint for a keyboard or something then you won't be able to customize the mouse profiles or use horizontal scrolling. However, I don't really need the software for anything so I just don't use it.
So basically, I prefer the TactX. It has a few flaws, but overall I think it's a better mouse than the Sentinel. The problem is really the price. I bought the TactX when it was on sale for $40 from Dell, but the regular price is $100 and I certainly wouldn't pay that. On the other hand, you can find the Sentinel Advance for around 40 bucks at a few different online retailers. I got mine at NCIX after pricematching it at BestDirect. If you don't want to spend a ton of cash then the Sentinel would be an easier choice, though if you're lucky you may be able to find someone on RFD or something who bought a TactX during the sale and decided to sell it off afterward. There are also other mice that I haven't tried. A few of the ones I'd look at if I were you would be the Steelseries Ikari, Logitech G500, Microsoft Sidewinder, and Gigabyte M8000X. Of course, the prices for those will vary. My personal choice out of the above would be the G500. Logitech is also releasing the wireless G700 which looks like it has a better shape, but it's also going to be over $100 and I don't think that's worth it by a long shot.
As far as Razer mice go, I wouldn't touch one with a ten-foot pole. I have heard many stories about reliability and driver issues and I don't trust their gear to last very long. Plus, their laser mice also use the Twin-eye sensor which has the issue I described above with the Sentinel Advance.
Edit: The TactX is actually
on sale again at Dell, though for $50 this time. It's also worth noting that it's identical internally to the G9x though the shape is different.