I was in the same boat about a year ago. I spent about a month owning both, but only kept one...Audio Tech's for me! There is just such a difference between the two, and each have a lot of awesome things about them and it really comes down to what you're looking for more specifically. I have a friend that went through the same experience as well and came out on the other side as me too! Haha. Let me tell you first though, I am far from an Audiophile. So please do with this what you will. I feel like I have an appreciation for good sound now though. For me, keeping the M50X's was all about one thing, the clarity that was still fun. I can't quite refer to things like mid-centric, or the trebles rolling off, or to what frequency the bass hits, but I can tell you in laymen terms that they were incredibly clear, yet fun for the price. I also have the Sennheiser 598's for this reason. Anyhow the M50X's are in my opinion, a very good value. I got the new special edition blue and brown ones, which I feel to be really really good looking headphone, and I have gotten many compliments on them. Not that that is a big deal to me, but they do look that good! lol They feel very solid. I feel like you could drop these things and really not be overly concerned about it. The plastic feels really solid and the pads and headband are nice and soft. The ear pads are really quite comfortable for me as I have worn them for several hours without any discomfort whatsoever. When you first grab them and move them around you will be assured that these have been built well. I really enjoy the 3 foot coiled cable that comes with them the most and it comes as well with a 3ft straight and the 9ft straight. Now like I said, the sound of these are really true. I feel like there is never a time where I feel like the highs are sharp or the lows muddying up the middle. They just sound super clear with just the right amount of what is needed to truly enjoy what you are listening to. The soundstage is probably the one area that I feel like they might lack a little, but I feel like I am just looking for something to pick at. They are good but not great for gaming as well.
Now for those V-Moda's....Everything in me wanted to keep these headphones!!! But when I would put the Audio Tech's on to compare, I just couldn't justify it. ( I was on a budget as well) Once you get hour hands on the M100's you'll really be impressed by just how amazing their build quality really is! I mean I was absolutely stunned at how cool yet insanely sturdy these headphones were. The one downside is that the ear pads were not really comfortable. That's not to say they hurt, but the clamp was a little tight for my taste and the pads themselves were just a little narrow and not very plush. I bought the XL pads as I kept reading that that was a needed upgrade. If I didn't have those, I don't think I really could have worn them at all. Just an FYI, but that is all relevant to you and your anatomy. lol . Now don't get me wrong. The V-Moda's are no slouch by any means, and you may very well prefer them, but to me they just didn't sound as good as the M50's. The M100's bass is a lot of fun!!! But just like most fun, it comes at a price. I felt like the bass was just taking away from so much else in the music. I couldn't hear the mids very well and female voices were hard to hear as well. They sound more "fun" than the M50's I would say, and you can use them without an amp and they still sound fun! The M100's actually sounded pretty good for gaming I thought, and the fact that you can just get the boom mic with them is super cool! And that thing works really well by the way! Like I said, everything in me wanted the Audio Tech's sound to be coming out of those M100's just because they were so awesomely built. I mean just check out the stress test claims on those bad boys and the fact that they give you a lifetime warranty on those things! They are that good! But unfortunately like I have said, the M50's just sounded so much cleaner to me, and the fact that they were almost $150 cheaper as well really pushed me to get the M50's. Now like I said, my friend went through the same thing and decided on the V-Moda's. So to each their own! I think he really just liked the heavier bass and the amazing build quality! It was nice too, because it gave me a second chance to try the V-Moda's about months after I had mad my choice, and again, I desperately wanted to like the V-moda's, but again, I was assured that I made the right choice for me!
Sorry if this is a little chaotic, as this is my first ever reply to a topic as I feel like I am starting to be able to have an opinion on some things. lol. I hope this helps you a little bit!