I am a Garrett fan, been using them for about 50+ years and have worn out 3, I'm using an Ace 250 right now and it does an excellent job.
Now for the fun part, a couple years ago I sponsored a detector hunt for MineLab days, they furnished me with a lot of stuff including a small foldup detector. I made a lot of targets for the hunt including a detector with 1/8th inch welding rod, a 5/16th nut, and flat washer for the coil set, I buried it about 8" deep under some dirt and rocks, this was my top prize, OK. I had 22 people show up and almost all the prizes gone except the grand prize, then a guy I've for a long time comes up and asked what this funny thing was he had found with his MineLab detector. We, and MineLab, had a good laugh about using a MineLab detector to find a target for a MineLab detector grand prize, and everyone else walked over the target a bunch of times.
I guess the main thing to learn is take a bunch of different metal objects, put them in ziplock bags, bury them at different depths, and the same distance from some place like a wall, fence, etc, about 10 ft apart, and mark the spot with some type of sign, grade stake, survey flag, or? and practice, practice, practice until you learn what your detector is telling you. DO NOT dig up your targets, that's what the flags are for, what it is, how deep it is, etc. This is how I do detector classes. Hope this helps you have a lot of fun, good detecting, less frustration, and be able to help friends get started too.
DON'T forget to fill any holes back in before you leave the spot, and replace the turf if there is any. This is not only considerate of the land owner, but shows respect for others so they don't get hurt falling, and have a healthy respect for us detectorists. A good rule of thumb has been not to spend over $100 per inch of depth for a detector, some times you can get a decent machine at yard sales and pawn shops, get something that's fairly simple to learn and use, too many people buy the biggest, bestest high dollar machine, that some saleperson sells them, then find out that it is so complicated that they don't understand it, so it goes in the closet and never sees daylight again, keep it simple and not too expensive, you can always upgrade later as your experience gets better.
Hope this helps, be careful, be safe, enjoy a lot. >^..^<
Chuck S