There are several great coils, but it primarily depends on your soil type (high or low mineralization) and what kind of objects are you trying to find. I own several of the SEF coils, the one that stays on my MXT PRO pretty much all the time is the 8x6 SEF Butterfly which I have used for years,(I am thinking that is what the previous comment was referring to also) I also have the SEF 12x10 butterfly coil which I use when I want to expand my sweep coverage. I have found the SEF coils to be quiet and stable, although if you think the MXT is noisy you may just need more time with it to get the setup right as it is very powerful and doesn't need high gains to get you good depth. I have used the Whites 4x6 DD shooter coil and like it alot although it seemed pretty limited on depth as it is so small, but great target separation.
I prefer the Whites D2 10" DD coil over many other larger coils as it is light and quiet but gotta admit, its the one I sold to buy the SEF 12x10. Smaller targets generally need smaller coils, greater depth generally needs larger coils. I live in Oregon where there is high mineralization in the soil (lots of magnetite) so I prefer DD coils over concentrics so I can get a bit more depth and when hunting in higher density trash areas the DD's help with target separation.
For my small coil I am currently running the Whites 5.3 eclipse concentric. It is very smooth and quiet.
Good Luck, I think you now own one of the best all around detectors ever built by anyone. I have owned many higher end detectors, got tired of all the settings you needed to mess with and went back to the MXTPro so I could grab it and go knowing I had all the horsepower needed to run with the big dogs in any ground, with one of the finest ground balancing systems ever devised.
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