I like both games, honestly. I played Miscrits first before ever knowing about Monster Galaxy, then again I've played many Broken Bulb Studio games long before Miscrits came out. I've been on Gaia for longer than that. Aside from those two points, I'll break down what elements I like about both games.
Miscrits: With Miscrits it has a bigger adventure to it. More story, and more evolutions. I hate the TP system, but they are doing away with that in the next big update with Volcano Island, their fourth map. They do a lot of maintenance and it shows. They try to keep players interested by giving them hints and clues about updates. Not saying that Monster Galaxy doesn't do that either. They are also more active with their players, such as with the forums. They keep them regularly updated every week not only on their forum, but on their page as well, and within the game. Sometimes we don't get that with Monster Galaxy, and it's up to us to figure it out first. The thing about Miscrits over Monster Galaxy is the rarity. Some are very common to find, others are rarer. It's a more open area to explore and some players like that sort of interaction. I do personally, and it makes for a different experience. As far as art work goes, Monster Galaxy has them beat. Not saying that I don't like some of the work Miscrits has done, but in comparison, it doesn't even hold a handle to Monster Galaxy.
Monster Galaxy: With Monster Galaxy, it's more collect than story. Sure there's a story there, but it's not quite as defined as Miscrits. The quests seem more like driven. Go here, do this, capture this, etc. Which is alright, but eventually you're gonna run out of things to do until you wait for more. I think that's why some people prefer Miscrits over Monster Galaxy, mainly because of the PVP. It's more involved, and players get a bigger thrill from it, plus it gives them something to try and aim for every week. Whether it be a Miscrit they don't have yet, or one that they might want another of. While Monster Galaxy is driven mostly by Black Gold. Players want it, but they must first go through an elongated process of capturing 74 different Moga in order to do that. Which is great, since you get rewards, but at the same time, players don't want to waste their precious Starseeds they collected first. I think that's another thing. The capturing method. While it is very easy to capture a Miscrit(poisoning it is my preferred method on both), the percentage can always be 100% on Miscrits, no matter how rare it is. With Monster Galaxy is primarily based on luck. If you run into a Legendary it's all about luck. If you run into a rare on Miscrits, it was about how much time it took you to find it. So both have their challenges. As stated before, Monster Galaxy blows Miscrits out of the water with art. It's fantastic, brilliant, and very aesthetically pleasing to the eye. The Moga, while some based on items right here from Gaia, aren't exactly myth-oriented, though I believe they stepped up their game with that in Zodiac Island, and are also working on that as well with some of the newer Moga. Either way, both are enjoying. Also, the music on Monster Galaxy is better. Miscrits lulls me to sleep sometimes.
There's my analysis, take it however you want it. I'm completely unbiased towards either games, and I do play both every day. Both are fantastic creators, and they deserve recognition for their work.