Pass on the LP2. It's not a great headphone, not terrible but the m50x is much better performer all around. So this come down to between the Custom and the m50x.
1. Build quality. The m50x is built like a tank. I've honestly never seen anyone break one through normal use. The original m50 yes because the cable wasn't detachable, so connections get loose sometimes. That's nothing out of the ordinary though. I've only seen the Custom once in person and from what I remember the build quality was also very good just like other beyerdyanmic products.
2. Audio quality. This is pretty subjective. The M50x is a has very good bass. It is full and well controlled. I felt that it was pretty smooth throughout the frequency range. The beyer depends on which setting you have that bass switch on. It can be overpowering to some if you have it in a higher position. I think my preference was on 2 when I listened to it. Beyer also has a rep for pretty harsh highs. Some people can't stand it because they think it sounds like nails on a chalkboard. Some love it because it gives headphones a sense of air and space. I don't remember much else about it, but I do remember that it was a good headphone.
3. Price. Customs run $200+, the m50x is around $140-$150.
Another headphone that I like that is comparable to these two and maybe slightly better is the shure 840. It has less bass, but I feel that the rest of the frequency response is better. It runs $200 msrp.
Personally I'd go with the m50x and use the extra $50 to pick up a headphone amp or something to go with the m50x. I feel that it will go well with the type of music you listen too and it sounds great with video games.