The Buderus is the best, in my opinion, but installing a condensing boiler means you have lower temps (138 F instead of 180 F).
- This will work great if your installer understands hydronic separation (Caleffi makes a great one) and outdoor reset.
- As with most things, it's more about the installation than the boiler.
Regarding switching to a gas boiler, gas may be a little cheaper, but the cost of changing over could offset that completely.
It really depends on your local prices.
For more information:
Read Richard Parker's Q&A "Can you help me select a high efficiency furnace?"