The Surly is the bench mark as the original production fatbike, some other makes are better for some types of riding, some are not, Surly Pugsley is still the most versatile frameset using 135mm so can use any hub set up, SS, gears, IGH etc, also it has options to take racks if you want, I have just bought my 3rd Pugsley frame to build a new Super Pugsley over the winter for next year
Real comfy flexy frame set with geometery that lets you get away with front end slides etc, My Pugs with the offset 29+ Krampus wheels makes my Karate Monkey a bit redundent now, I have not ridden anything that has made me want to upgrade for riding trails and the coast. Weight is an over talked thing with fatbikes, Pugs frameset though is light for what it is,
It has the shortest chainstay for a 4" fatbike (only 5mm shorter than an On One) still the best fatbike for the money i have ridden for both MTB type riding and beach/ moorland peat and areas you take them where a regular MTB would be a struggle or unrideable.
Fatbikes are not a replacement for a regular MTB, Something some folk keep banging on about...
Some white and black frames from a production run had a frame cracking issue at the seat tube to seat stays, which Surly have warranted and replaced,
29+ - thats the fatbike for regular MTB riding areas