David,
I feel a lot of which is better is how well you understand them and your hearing. I say hearing is because the Sovereign is louder plus the tone stay that of the last target with the Sovereign, the Explorer changes quick and back to a normal threshold which some cant hear.
Both are excellent detectors and both will do well, some that have used both will prefer re the Explorer while others go from the Sovereign to the Explorer only to come back to the Sovereign. Others will go from the Sovereign to the Explorer and stay with the Explorer, myself I have both and find the Sovereign is the one I am more comfortable with with the Sun Ray meter for IDing my target. I find I dig less trash verses good coins with the Sovereign. Maybe this is because the meter is reading what I am hearing while the Explorer you may hear a good signal, but the meter is showing trash as the threshold has to come back to get a ID.
As far as which is deeper I feel the Explorer should be, but I have dug just as deep with either one.
I find the Explorer you can do more with and can separate your quarters from you dimes and copper pennies, but the Sovereign put them all together in one number.
Signal comparison on actual targets in the ground find that 99 % of all target the Explorer sees as good the Sovereign will too, but it is not 100% of them.
The Sovereign is a turn on a go detector while the Explorer you have to set for you area and how you want to hunt.
Rick