I have been using the Uni Ball Vision Elite for a while now. I'll just state the pros and cons so that you don't have to waste time on reading a lengthy review.
Pros: 1. Low friction when writing on paper. Will certainly help you in improving your speed. 2. The grip is superb. 3. Visually appealing. 4. Shock proof. Works well even if you drop it from a height on to the ground.
Cons: 1. Cannot be refilled. You will need to get a new one. 2. Expensive.