Duncan Bearing King is what I would generally recommend. It comes as a fixed bearing, but you can remove that top and replacing it with the included bearing tip. I have found the bearings could use a good cleaning, giving you a lot more spin time.
These retail for around $12-14, making them an ideal starter top. It is what I recommend.
After that, you tend to move to the Spintastics Trompos, which I haven’t gotten yet. The steel tips are better than the Duncan plastic tips and start at around $20 and can go up to $40 depending on the exact model. For starting out, I wouldn’t go more than that.
The next step would be Strummol8, which is actually coming out with some mind-blowing moderately priced spin tips, although the Sophia and Guilia are considered to be the best. I have a Sophia but I haven’t even thrown it yet.