I managed to pick this up in the indie music deal last month and have dabble din it occasionally, but not really got the hang of it. 
 
When i saw it was one of todays steam challenges my initial thoughts were  
"Hurray a game i dont need to buy, i can do this" 
 
Now my thoughts are 
"I fucking suck at survival mode, and have no idea which songs could get my close to that 3.7 mil mark" 
 
Any hints, tips or suggestions for songs?

I've played quite a bit of the game and still can't really commend any specific songs for survival. I'm fine on the "hard mode" but I feel like for survival the game really ramps up the difficulty.

A lot of techno and trance stuff lasts a while and can cause a huge amount of low-level enemies to amass. 

Stockholm Syndrome by Muse should easily get you the achievement. I'm sure there are many other better choices, but its a pretty good song to play to. Might be a little difficult. Definitely suggest playing with a gamepad.

" A lot of techno and trance stuff lasts a while and can cause a huge amount of low-level enemies to amass.  "

You would want to use music that is constantly playing. Don't use anything that has any breaks or use anything that goes into a softer tempo. For example I use heavy metal songs like Lamb of God and Devildriver. They stick with the same rhythm and tempo throughout their songs.

iir leveling up will help you quite a lot, also I think if you don't shoot for a while it'll increase your multiplier 

" @Tairoku said:

" A lot of techno and trance stuff lasts a while and can cause a huge amount of low-level enemies to amass.  "

That sorta seems like what was going one with the Wolfmother stuff.   Maybe not to the same degree you are talking about, but there seemed to be a ton of enemies at times, and the bosses were constantly shooting. "

Confusion (Pump Panel Remix) by New Order.

" Good job on the recommendations guys, this is probably the hardest of the steam challenges so far i think! "

" @metalhead87 said:

" @Tairoku said:

" A lot of techno and trance stuff lasts a while and can cause a huge amount of low-level enemies to amass.  "

That sorta seems like what was going one with the Wolfmother stuff.   Maybe not to the same degree you are talking about, but there seemed to be a ton of enemies at times, and the bosses were constantly shooting. "

I find the higher amount of bass, the larger amount of low-level enemies. So, I'll listen to NOISIA and Unknown Error whenever I want to crank out points. "

nothing soft!  Either some good electronic/techno, high BMP means your shooting more. Maybe some metal if you prefer.

I dunno, I hit one of the highest ranks a while back so i start with a ton of bonuses which makes it easier. 
Tip- Play on Suicide difficulty. You get higher scores much easier on higher diffs.

Alright i finally managed to break the challenge score (almost doubled it in fact if i hadnt been so dumb) 
 
I managed to get it by starting on  
"Thoughts of  a Dying atheist" by Muse from the "absolution" album 
I then finished that song as well as the next "TSP" and eventually ran out of lives on the final track "Rule by Secrecy" 
 
Final time of just over 5 minutes and final score of just under 6 mil. 
 
Now i am terrible at this game so if i managed to get that on those 3 songs then just about anyone can! so anyone having issues be sure to give that a try!! 

Choose fast paced songs. That's the big one. I used Anamanaguchi and lasted almost 2 hours.