I'm an Eheim Jager user. For me, the best heater out there...but they are long. Also strongly agree with at least two heaters. No matter what brand you go with, they do fail. And if it's one heater dying, at least the other one will attempt to maintain temperature. If it's a stuck ON failure, this is why you want to get a temperature controller. I'd recommend either a Ranco or Inkbird. Both are quality controllers, but you do need to get a truly waterproof sensor.
Here's the chart for Eheim's. Don't know what your garage situation is as far as being heated, but my first though is two 250's, if they will fit. If it's a heated garage, two 200's would be fine. Eheim's are long.