Been Fat Biking since 2010, if I wanted a 4″ wide tyre’d Fat Bike and I was starting now with all that I have learnt and I had £1500 burning a hole in my pocket then the On One Fatty Trail with the Bluto’s would be what I’d buy for sure.
If later on you want a nicer say custom titanium frame then have it built around the Trail Fatty as it would make a great donor bike.
If you wanted even more floatation with 5″ tyres then you need to look either custom or the Moonlander