Right now I have the Garmin 35 which is the cheapest, simplest version of the GPS watch that they make...still, it has everything you need: pace, mileage, splits, altitude, heart rate, etc.
My only complaint about the watch is its poor battery life. After a full marathon it is depleted to about 50% battery, but this issue is not really a huge concern.
That being said, I know the more advanced watches have interesting features like training insight, stride analysis, cadence analysis, etc.. Have you ever used any of these features or do you just concentrate on the main data that you can get from any watch? Is the $300 watch really worth it vs the $100 one?