The Lowrance LSS-1 imaging transducer. Rugged, yet with a smoothly fluid low-profile, low-drag design, it's made for multiple mounting locations - transom, transom step, jackplate, even trolling motors (with a simple, inexpensive adapter option). It also has a built-in water temp sensor.
For transoms, there's a smarter-designed, stainless steel mounting bracket with a kick-up feature for water hazard strikes. Damage the bracket, and you simply replace it (not the entire transducer) inexpensively.