For me it depends on where you hunt more than what you hunt. I currently use the stock most of the time. If at the beach or in deep loamy soil, the 17 is my goto for depth (and coverage at the beach). I only use my Coiltek 5x10 in HEAVY trash- I find that going slow with the stock works quite well in moderate trash. I'm the opposite of Jason/Enid in that I use my 17 much more than my small coil- but again, I think that's a function of where we hunt. Bottom line is that I think you should consider where and type of soil you will be hunting when deciding on which coil to keep/buy.
Sorry, I don't have a recommendation for a backup machine. I would think that it all depends on how much you want to spend.
Sorry, I don't have a recommendation for a backup machine. I would think that it all depends on how much you want to spend.