They all have their advantages and disadvantages, Transom mounts are easiest to fit and if you don't fish in deep , ie 300ft+ water then it'll be fine. Just have to be careful with the position so that it works at cruise speed.
Alternativel;y if you really want to see detail in deep water then a 1kw thru'hull is the way to go . I have had a previous boat that had 2x 600w transducers , one thru hull and one shoot thru' the difference between them was quite obvious . The shoot thru worked better at speed but the thru' hull had a clearer picture at trolling speed.
On my 265 express I have a 1kw thru hull in a high speed fairing block hooked up to a Furuno 585 and it's the best picture I have seen on any boat at any speed!