I use 80-20 or 75-25 steams to electrics. I prefer electrics when I require stealth. Typically when shooting at an escorted target and for the first shots in a massed convoy attack. Also when making a first shot at a warship (admittedly rare, I prefer to let them go rather than take chances).
I prefer steams for all other situations. They're much faster, which makes maneuvering your boat simpler, especially in snap-shot situations (like attacking in horrible weather). Their speed and shorter path to target minimizes targeting mistakes, they have much better range, they don't keep me hanging around the target for as long, and they are rarely dodged by merchants who aren't already dodging (and in those cases, I think my aim is off due to AoB errors). I also like to set them shallow (usually 2M, sometimes 1M) so that I can actually see the path target of my torpedoes. It lets me know if something's wrong with my aim (e.g., forget to clear the datapad-
, or if my calculations of speed or range are slightly off).
Currently, in my IX-B, I like to sail with two front torps as electric, one rear torp electric. I keep two front electric spares, and two rear electric spares, so most of my reloads are steam. I just like having the electrics on hand in case a juicy target pops up that is, or is escorted by, a warship. Otherwise steam does it for me!