Here's my two cents if you care. I picked up both pro versions during the 10 cent sale a few weeks ago (previously just used the free versions):
I'm only going to list some differences I found, since they both function similar.
Soundhound:
- It tags a bit faster, IMO.
- It has trouble recognizing live tracks and will frequently tag them as the recorded version (Shazam doesn't seem to have this issue).
- A nice pro is you can sing or hum a song, and it will (usually) recognize it. And I suck at singing.
- I do like that it gives the album name at the top of the screen, while Shazam only gives the track and artist, and you have to scroll to the bottom for the album name. Also it's a few more presses in Shazam to get to the actual album information (such as all the tracks that are on the album).
Shazam
- I like the interface and colors better (Personal opinion, plus I think it looks "snazzier" while tagging)
- Allows you to send the tagged songs to Pandora and Spotify (sorely lacking in Soundhound)
- Has a nice option to tag on startup, which can save a valuable second or two while trying to catch the end of a song and is very handy in the car, as it saves having to press an additional button.
- Has kindof a cool feature where it scrolls the lyrics (karaoke style) while the song plays.
They both offer similar functionality as far as buying MP3s (AFAIK, both are limited to Amazon's MP3 store), and they both offer discographies, biographies, lyrics, tour info, etc.
I did notice (just now) that Soundhound has a nice "find this song on albums" thing that Shazam is missing, that will give you every album that the song appears on (that's nice, in case it's on a soundtrack or multiple albums).
I personally haven't really found a song that one will identify but the other will not, other than the aforementioned issue Soundhound seems to have with live tracks (for example, if you tag
this live Alter Bridge track in both apps, Soundhound identifies it from being from the album "Blackbird" while Shazam correctly identifies it as being from "Live in Amsterdam").