I always try and buy the best detector that I can afford for the area that I am going to be detecting in. Just starting out I would recommend getting one that will let you grow into it but not be to overly complicated to learn. Some of the brands that have multiple configuration menus, I would put in this category.
After you have a couple models in mind, go on youtube and look at the various review of these models and the setup. You may find models that you just don't feel you would be comfortable with for whatever reason so they can come off the list.
If you have a local dealer or someone in your area, ask to see their detectors and see how it feels in your hands.
Don't be afraid of asking questions on here.
Ray