I've been looking for a lightweight softshell that doesn't break the bank for spring/early summer treks, and potentially for hiking across South America this summer. I wound up trying both the MH Offwidth Jacket and Patagonia Simple Guide. I'm fairly small (5'7, 34" chest) and ended up getting the MH in Small and Patagonia in XS.
Fit: Both jackets are sized nearly identically - same hem width, back length, armpit-to-armpit width (20" armpit-to armpit, 19" hem width). The Simple Guide has 1" longer sleeves and a slightly tighter bicep area. When worn, both expectedly fit the same, with a fairly athletic cut and room for a fleece layer but not much more.
Features: Once again, nearly the same features: 3 pockets, hem drawcord, velcro cuffs. The Offwidth has a neck drawcord. The Offwidth has a slightly heavier soft shell material and as a result weighs about 4oz more than the Simple Guide.
Material: The jackets differ mostly here, with the Offwidth having a slightly thicker, more windproof softshell than the Simple Guide. The texture of the Offwidth is thicker as well. Both have tons of stretch and do not have a fleece backing or membrane. The fabric of the Simple Guide is much more breathable -- probably the most breathable soft shell I've owned -- and is less crinkly and falls more naturally when wearing (think silk scarf).
Styling: I love MH but one thing they need to work on is the styling. I would not wear the Offwidth around town -- it has loud, white Mountain Hardwear logos on the chest, sleeve, and even on the velcro cuffs. Even worse, the zippers stick out at a weird angle to the front AND to the side of the jacket due to the construction of the zippers -- WHY MH WHY?? In contrast, the Simple Guide just oozes with style with an understated logo on the chest and tasteful zipper drawers. There is no comparison here really, the Simple Guide wins hands down.
In the end, I found that both jackets had a nearly identical feature set, and both clock in at $120 retail. I sided with the Simple Guide primarily because the soft shell material was lighter and more breathable, which is what I'm looking for during spring and summer. Also the styling may be a deal breaker for some, for me I spend 95% of my time NOT hiking so this was a factor as well.