I'd take serious issue with the Rena Excel recommendation, esp. over Tronic. If you do a search for all the threads regarding heaters on a variety of fish boards, you'll repeatedly see good experiences with Tronic and Ebo Jagers. (This is not to say that no one has ever had a bad Ebo or Tronic.) You won't find the same level of recommendation for Rena heaters. They just aren't as well made or as reliable.
Jim
Jim