Mouse: Dell USB
I'd be lying if I said that moving to a standard two-button Dell mouse after using all of these fantastic gaming mice wasn't a little painful. I immediately missed the extra flexibility of a purpose-built peripheral in all of the games I tested, especially after having the flexibility to bind mouse buttons to my favorite weapons, push-to-talk, or perform even more creative tasks, like replace key commands for certain in-game functions. I used the scroll wheel-click on the X3 to open my map in World of Warcraft, for example, instead of having to press M.
The core question, though, is whether an expensive, premium gaming mouse will help you game competitively. Unlike keyboards, where the answer depends highly on the type of game you play, with mice, it really depends on how heavy of a gamer you are in the first place.
Over time, I didn't have a problem with the Dell mouse. All of my games were playable, even at the same play level as with the premium mice. The problem with using a low-end mouse is that some games automatically make use of gaming mice with multiple buttons for certain default actions, and without those buttons you miss the features that come with them.
The one issue I have to single out is DPI sensitivity. Laser sensitivity and DPI have become almost like a measure of clock rate in a processor discussion. More is marketed as better, and each manufacturer's goal is to have the mouse on the market with the biggest DPI numbers and the best tracking engine. Frankly, more DPI doesn't mean a better mouse. Even if you have a mouse with insanely-high sensitivity, most gamers won't actually play with the sensitivity turned up that high. I found that on most gaming mice, the bottom and top DPI settings were throw-aways. Usually, I wound up in the middle or on the high-end. For mice with only three settings, I could see vacillating between the mid-to-high end in games where precision is required (if you enjoy playing a sniper, for example). But in most situations, don't spring for a mouse just because the DPI sensitivity is higher than its competition.
If you're a novice, laying down $70 to $100 for a high-end gaming mouse won't make you a sharpshooter, but once you're used to using a high-end gaming mouse, you'll never look back. If a $100 mouse seems gratuitous, the range of features in price brackets all the way down to $40 (or lower, if you can catch a sale) won’t disappoint. You may not instantly be a better player, but you'll feel better about your gaming, and that'll make it easier for you to improve.