Sorry for the late reply. I typically prefer the mono releases that were originally recorded in mono. For instance, Bob Dylan's first record, it was originally recorded in mono but when it was released on cd they did a fake stereo mix where they just separated the vocals to one side and the music on the other. House of the rising sun on that album is awesome in mono, but the fake stereo mix sounds thin and especially hard to listen to in headphones. Until recently, you couldn't even get the mono mixes for Dylan except on vinyl. Early Beatles albums are similar, like With The Beatles, vocals on one side and music on the other. The original mono mix is much more full sounding. Stereo wasn't mainstream till the mid 60s, so a lot of albums are like this. Then some, like The White Album, have a mix for both stereo and mono because a lot of people still had mono rigs, but stereo rigs were becoming more common. I actually am mixed on this album, some songs I prefer mono and some stereo. Strangely enough, you can find the opposite sometimes. Abbey Road was only recorded in stereo, but there is a Brazilian mono mix, but it's just a folded stereo into mono, so not a true mono. It sounds terrible by the way, I got a bootleg ripped version.
I haven't heard the hd-25 myself, but it gets good reviews. For under $200, I'd look for used to get bang for your buck, there are a lot of good deals in the FS/FT forums. I've seen a lot of HD-600 and even HD-650s go for at or around $200. If you are wanting something more open and forward sounding and easier to drive, you can get the Grado 325i for $150-200 usually. The Grados are more polarizing, some don't like the house sound others love it. I think the 325i is the best headphone under $300 you can get, I like it better than the RS2 and PS500. Good thing about buying used is that you can usually flip them for little to no loss if it's not your flavor. If you do end up getting a higher impedance can like the Senns, I suggest saving your money for a Bottlehead Crack kit. I built it over a weekend and it is an amazing amp for Senns.