I really prefer floating de-icers. They just de-ice the top (duh), as opposed to heating a column of water, which is what a sinking heater will do. This is important, because in the winter, there are layers of water at different temps. fish generally stay in the bottom layer, where it is warmest. A sinking heater will create a current of rising warm water, and sinking cold water. fish have to use much more energy to try to stay in one temperature zone. the more energy a fish uses during the winter, the faster their fat reserves are used up, and they may not have enough to make it to spring, or at least will be weakened and prone to disease. In your case, a 100 gallon pond it will be important to get a good one, or the pond may freeze solid!
I don't have a brand preference. I have tried several, and can't endorse any of them. They either broke in one season, did not work properly below a certain temp. or... I don't recall, but none have made me completely happy. I'll be shopping for a new one again very soon also.
