Most importantly, what and where

What and where are the only two things to consider when choosing a metal detector.
This advice is not just for people new to the hobby of metal detecting because one of the biggest mistakes you can make is using a metal detector not suited to detecting what you are searching for.
Using a metal detector not suitable for your intended search areas will set you back and possibly cause you to give up on metal detecting.
Metal detector companies and dealers have a wide variety of metal detectors and accessories that can and do make a difference, assuming you choose the right one for the job.
I had to start all over again when I first got into beach hunting, the equipment I used for land hunting was good but not good enough for saltwater beach hunting.
Constant chatter due to the salt content on the lower beach made lower beach hunting a nightmare.
Having to lower my sensitivity control down to counter the salt content prevented me from detecting mid to deep range targets using my favorite inland metal detector.
I searched in all metal mode and tweaked other controls until I had finished my research into what metal detector I needed to use around a saltwater environment.
My fortunes turned around quickly using a multi frequency BBS technology metal detector known for its ability to operate smoothly at saltwater beaches and detect small silver targets.
Old fashioned research studying what metal detectors work the best at detecting the targets in the areas I intend to search paid off.
Back in the day I predominantly searched for Spanish silver treasure coins at shipwreck beaches along the Treasure Coast of Florida so I had to have the right tool for the job.

Horses for courses my friends, the what and where are the important factors no matter  where you intend to search and what you hope to detect.
We have never had so many metal detecting equipment choices to choose from as the hobby has become more popular, even with more choices the right choice still has to match what and where.
If you want to see Bobby dazzlers in the bottom of your scoop basket at tourist beaches, you'll need a metal detector that can handle the salt and detect small gold.
Believe me, if you can detect small pieces of gold jewelry you will have no problem detecting large pieces of gold jewelry. 
The best of both worlds is a metal detector known to detect a wide variety of targets in a wide variety of areas.