Mostly anything above 200BPM is good. Image Material is very good with it's guitar and so is DragonForce. Basically anything fast with an electric guitar is good. Also fast paced classical is pretty good. Basically anything fast.
I don't really know the answer honestly. Mostly i'm looking for the songs witch it's so awesome to map by my skill. Right now i'm forsing to rank sakuzyo - Refel. I really like sakuzyo traks especially some of his famous tracks (AXION, Storia feat. xi etc). I'm also looking for fast songs witch makes a challenge among players example L.E.D.-G - BITTER CHOCOLATE STRIKER or t+pazolite - Call me it. (500 Tortures). In other words, I make challenging maps. Thats all!
I look for songs with varying or interesting rhythm (Breakcore, hi-tech) Because they're on both sides, mapping and playing-wise very interesting in a rhythm game - also offers a brighter field of difficulty.
I look for consistent songs (Hardstyle, quaver, etc.) In case I want to relax a bit it's more comfortable to play these songs.
50 bucks that will be the option with the most votes within the next seven days.
of course i would choose songs with interesting rhythm and songs with good vocals (yeah we need more utaites map xd)
songs with interesting rhythm may give a nice variety when mapping. could give more flow to the mapper and to the players when playing it. while songs with good vocal would give us eargasm from the vocalist's voice xD. this type of song could give the mapper to do more variety too on their maps!
let's clarify my choice: I generally take whatever song I find particularly dear to me, either because I like a part on it or because it gives me a certain vibe. That emotion is the basic ingredient for the map I will gonna make later, so I can't map well unless I have any feelings towards the song.
In most cases, good lyrics and different rhythms together make up for that, but I encountered quite a few songs that were literally the same thing over and over yet the map came out well anyway since I liked that repeated part. (BPM in the end doesn't matter)
I'd say I'd pick up songs with interesting rhythm.
For the second choice, I scrapped it because there are songs with good/cute vocals but looow BPM (not mapped but Susume*Otome ~jewel parade~ - BPM 130), and songs with bad vocals but hiiigh BPM (Everything will freeze - BPM 240 - linked is the instrumental version, mapped by Ekoro), and I don't take into consideration what you call "my waifu", and I can't select one of the two, the first vote used.
Looking forward to more BMS. ...and some stuff with Gamegame (Groundbreaking track. Safe to mention and everything - way interesting it may feed some mappers and players' hunger for awesome works!)
EDIT: White star replaced with an asterisk just in case
I guess I'm out for real, but you can still see me in osu!Discord