I'd say pretty different cartridges the 2M Black & the Grado Sonata. My personal experience has been w/ the lower rung in these series : 2M Blue & Grado Gold Prestige, so don't know how 100% directly transferable to these. The obvious difference Gold vs Sonata is the housing, but otherwise they are similar engines. Blue vs Black, also better housing for Black, but also top of the line needle.
The Grado Gold - and I imagine the Grado Sonata - are going to be a lot warmer than the 2M Black. If that's very important for you, then the Grado. I personally liked the 2M Blue more than the Grado Gold. More speed / attack / rhythm. As pleasant as the Gold was - and could produce real magic on the mid-range sometimes - I could not accept a cartridge that couldn't swing. I also didn't find the 2M's to be too bright - though compared to the opposite extreme that is Grado, I could see why some might think different.
Either honestly is probably a good choice, but based on the above, best to decide what's most important to you & what compromises you're willing to make. Unfortunately it seems to me until you get to $1K+ for a cartridge, compromises have to be made.
