All of these instruments have their own merits, ask the sales reps to show you the different units connecting to your sonar kit. From my experience the Leica wins out because of the control you have over the output formats to the sonar. Topcon are primarly aimed at construction, Trimble at survey engineering and Leica at professional survey requirements. In this case you will defintily get what you pay for....

I can speak for Trimble and Leica. My money would be on Trimble. Leica is kinda like the Microsoft to the computer world. It's good. Used all over. Has many good applications. My problem with Leica are as follows. Their software programing is terrible and by far the worst, my opinion, in the business. Have to have multiple SD cards in case on fills up or gets lost or stops working or your working with the older systems that require a card in everything. Little plastic pieces are always the things that break on them that hold a wire or display or battery in place. I could go on. For me my money I would spend it on Trimble. You get what you pay for. I used Trimble/TDS for about10 years. The only problem I had with it was once I was working away from the truck and a rain storm came up and soak me and the equipment. Ruined my Trimark radio and the TCe Collector. Fried them both. Other than that I never once had a problem with software, little things breaking, or cards. I take that back there had to be a card in the 5700 and older receivers for static. The newer R8 units everything is in the collector or unit memory.