I've had a Marmot Hydrogen, Helium & Lithium.
I've had a WM HighLite, Badger, Kodiak SMF & Bighorn SMF.
I currently have a WM MityLite, Sycamore MF, Sequoia SDL & KodiakSMF.
At 6'2" & 200lbs I'm mostly legs so I like the hip/foot girth of the WM semi-rectangulars (named after trees). The Sycamore doesn't have a collar but whichever jacket I carry makes a nice collar and will keep me comfortable to about 15dF if I need it to.
Some folks are good with narrow bags but I like to have room to move. Plus as I get warmer I can shed clothes and they stay warm in the bag with me. With the big bags I can also get shoes and water bottles inside to keep them from freezing. Though the big bags weigh more and use more pack space it's a trade off that's worth it for me.
When you buy a WM bag you're paying for craftsmanship and the best materials available. If you're Hydrogen is a long model the girths are 64"/60"/40". Look at the WM spec chart compare to see where you want it bigger for the temp range you need.