The SRT is mechanical, has mirror lock-up, and is a perfect backup, or a camera to keep in the bag with a 24mm (while you have maybe a zoom or a normal in the other camera), or to use for special purposes such as tripod use, macro use, very-wide-angle use (you can mount certain very-wide-angle lenses only if your camera has mirror lock-up, and use an external viewfinder).

The other one is probably more pleasant for general use, being more silent, lighter, having an electronic shutter release which can help, and probably having a brighter viewfinder.

Mirror lock-up is very important if you do tripod work and if you care about sharpness. I don't know which are your other cameras. If I really had to choose and if this were the only SLR to have, I would go for the SRT no doubt because of mirror lock-up.