My Opinions (and replies to what people have listed as their fav....you can figure out who):
I hated Code3 sirens for the longest time, and I finally figured out why after realizing that I actually like their Wail & Yelp, and LOOOOVE their Hi/Lo. It's the air horn, I absolutely hate their air horn. To me, it's no better than a PA300 horn, which ironically enough, is a siren with only 1 fault, the horn.
The eQ2B horn is nice, in that it sounds like Grovers, BUT, the fact that they try to replicate the "squeak" of the air rushing through the horn at too low a pressure at the beginning ruins it for me. I love short taps of the horn, and with the eQ, you merely get the damn squeak, if anything at all...
Someone said they hated the Whelen horn. I'll admit, it's not the lowest pitch out there, but it's also not the highest, and to me it has a nice full bodied, sharp, gutteral sound. I realized this one day while driving through West Philly (and people wonder why working a prison wasn't much of a change for me, lol!). Wasn't even driving code, just sitting at a stop light with the windows down on a nice mid-spring day, and the HRN/SRN switch was still left on SRN accidentally. The light turned green, and the car in front of me didn't move for a good 3 seconds, so I just tapped the horn. The sound that echoed off the buildings was fantastic, IMHO. You're right, it's not the lowest, but it sounds damn good, and it works.
Carson is decent, but the sound seems a little....dull.....
Unitrol is pretty much tied with Whelen for first, and for the same reasons. My only complaint, which I've noticed mainly on the Deltas, is the same thing as the eQ horn. If you just tap the horn, all you get is a speaker pop. A split second later, you get the horn. It doesn't take long, but it's enough that if you just tap it, you don't get the horn sound. It is, however, effective for the random pedestrian who might not see you, but you don't want to deafen....