by ricedwlit
It really depends on what you are looking for. I own both (all in for each KS) and enjoy them for different reasons. In case it matters, I play each game solo - for CDMD I play with three investigators and MA I control 2 investigators. I have played CDMD with other people as well and it plays pretty much the same as when I play solo; I've not played MA with other people.As noted by others, CDMD is a lighter game and I've yet to have a game take over 90 minutes. There's a constant sense of tension as the investigators are vastly outnumbered, but this is offset by the whole push your luck + go insane and power up. Most games come down to a stunning finale where you are chucking multiple dice to try to take down the elder one and either succeed or see your people get killed / go insane. The ones that don't make it that far are when I push my luck too far and see someone get killed early by a swarm of enemies.
In contrast, MA is much deeper, with most of my games taking up to 4 hours. There are ways to shorten the game by only doing some chapters, but I like the experience so much that I'm okay with the time. The upcoming expansion in the recent KS says it will deliver shorter games, but that remains to be seen. The tactical depth for the game is amazing. Similar to CDMD, the investigators are immensely outclassed (not so much in number, but rather in how powerful the monsters can be), but in MA the goal is to be strategic in how you deal with things. Get equipment, run away from the monsters, lure them into traps, etc. It is really satisfying to make it to the endgame and have the investigators equipped with powerful weapons, armor, and artifacts. The crafting system helps you to customize what you get to what you want your investigator to do: get in close and fight monsters or snipe from a distance.
There are more scenarios in CDMD (6 in core game, two elder ones so 12 variations) whereas MA has just 8 (counting all the content + upcoming expansion). However, since a lot of the variability in MA is how the board lays out and when you see monsters + horror events, so I think both are equal with respect to replay. I've played CDMD a lot more often then MA (due to it being easier to get time at the table), but if I had to keep only one it may be MA.
In summary, a lot depends on what you want to get out of the game. Hope this info helps.