Everyone has an opinion here is mine. Depending on what type of detecting you do will determine what you need. If you mostly hunt saltwater beaches and need a diving detector I would recommend any of these: Minelab Excalibur, Whites PI pro, Fisher CZ 20, Garrett Infinium, White's Beach Hunter ID, Tesoro Sand Shark. All of these detector do a great job. If you want one that discriminates (knocks out trash) then CZ 20, White's Beach Hunter ID or the Excalibur is the one for you.
If you need a detector and don't plan on using it underwater I would say any of these: Minelab Sovereign, Eric Fosters Goldquest SS, White's DFX
I have used all of these with great success. But it really doesn't matter which detector you pick. What matters the most is learning how to use it properly. Most people swear the detector they use is the best. I think they just got use to it and like it better than the one they didn't like or didn't learn to use properly. Don't be fooled by all the hype most are just advertisement claims exaggerated to boost sales.
It is true that some are more sensitive and can go deeper than others. Some have ID meters, tone ID, depth meters, better pinpointing etc. But there really is in my opinion NO BEST
detector, all have there good points and bad.
The best way to decide is read the forums. Decide what type of hunting you plan on doing and get some advise from people who actually use them.
Like most of us you will have a arsenal of detectors to pick from not just one.
Which ever detector you pick. Learn how to use it well. It will give you years and years of enjoyment and some loot to boot
Happy Holidays and HH
Steve