Do you have a price range that you are thinking about? In freshwater you can use just about any waterproof detector but saltwater is a whole different ballgame if you plan to hunt in the water or wet sand. Multi-frequency machines work much better in saltwater but they are generally more expensive. Most machines will do okay in the dry sand.
You can get overwhelmed very quickly with all the brands and types of detectors. Everyone has their favorite but that does not necessarily mean that it will be the one for you. I have used a lot of different detectors from high end to low end and I have been always gravitated towards Whites machines. They are good machines, made in the USA and their customer service is top notch. I had the MX Sport which was waterproof and a great performer but it was a little heavy for me. I have RA so even somewhat heavy machines hurt me if I detect for any length of time at all. I now have a Quest Pro detector and I am very happy with it. It is light, fast, deep, ID's very well, and is waterproof to 16 feet instead of 10. They are not as popular her in the States as they are in the UK because even though they are a California based company, the detectors are made in China and that turns some folks off. Mine performs very well and I have been in the water almost every day lately and have had no issues. Once you decide what price range you want to be at then choosing a machine will be much easier. Some will tell you to get an entry level machine and try detecting before you invest a lot of money but if you want to get serious about detecting then you will probably need to upgrade pretty quickly. My opinion has always been get the best machine that you can afford to eliminate that quick upgrade. If you stay with the popular detectors, you can always sell them if you don't like MDing and you won't lose a whole lot of money. Get a cheap machine and you will have a hard time selling it. You will get different opinions on almost every topic about detecting and that is just the nature of the beast. Please feel free to PM me if you have any other questions and I will be glad to help you if I can. We are probably 2 or 3 hours away but if you ever come tube the Guadalupe, then you will be in my neighborhood. Good luck with your dedision.
Pesc