I haven't used the Garrett Seahunter so it would be unfair for me to comment. I can tell you that I have had very good success with my Excal 1000. If you go for the Excal insist upon getting the new yellow headphones as the blue ones don't give great sound differentiation. This is a auditory tone machine so sound quality is critical. Upgrading my headphones to GG's or comparable is the next step in the evolution of my Excalibur.
I will say that I looked at the Seahunter, the BHID, the surfmaster and the CZ20 as alternates before taking the plunge and spending mucho moola on the Excal 1000. Based on my research, which was geared towards my conditions the Excalibur 1000 was the best choice in my mind. It took me 3 months to make up my mind, which is about the same amount of time that I take when buying a new vehicle.
So far I think I have made the right choice even though I am on record as being dissatisfied with the fit and finish of this unit and Minelab's inattention towards resolving what I see as design flaws.
What is important is the brains of the unit and the coil arrangement. I have to give Minelab top marks in that department and that is why I am sticking with the Excalibur 1000.
Do the research, make the best possible decision and then get out there and swing. If the coil doesn't go over the target, no machine will find you the gold. You have to train yourself to the machine as well or you will only have lukewarm results.
Check out the Goldenolde.com for some good advice as well as the advice from the members of this forum. We are all still learning and hopefully always will be learning as that is part of the fun of this hobby. Keep it fresh and keep it fun!
Cheers,
BDA