I've been using Stockfish 8-64 with my version 12, and it runs circles around the default Fritz engine (thanks to Mike Runnells for help with this). I imagine I'll end up doing the same. According to Mike (who has a number of engines) Stockfish 8 is almost as fast as Houdini 6, which in his experience is the fastest at the moment. Remember: Stockfish is free! Simply visit www.stockfishchess.org and start your download. Mike also sent me a link to a site benchmarking current engines - one of the posts I'm backed up on.
I'm really interested in how others use their engines and software. I've been using Fritz to put my games into a database (I have a small one for Rochester players as well - available to anyone who wants it) and analysis, opening development, tactical and game studies, etc.
After I break this out I'll tell you how I like it and how it compares with Fritz 12.