The MLPD is weird. ive only ever heard bad things about them and oftentimes they were described as 'cult-like'. that's probably because get the entire inheritances from deceased memberes and have, too my knowledge a lot of nepotism as well as pressuring members or just interested people into donating. this is also evident by the fact that they are an insanely rich small-party. what they do with the money idk but the only political activity is see from them is electoral campaigns/hanging up a lot of signs. i do not recommend the MLPD
The DKP is very solid. very well central-democratically organized and has a lot of very well-read marxists. their stances/electoral campains are principled marxist leninist and so a good job educating it's members and environment. the dkp is one of the very few based organizations in germany so it's a good idea to organize with them