I'm not really a fan of howlers for bringing them in (although I HAVE watched Randy Anderson do it hundreds of times on his videos, so obviously it works for some guys), but the only one I really use is the Primos diaphragm calls.
I have a couple dozen howlers, and the diaphragms are really all I use with any regularity.
My 2nd choice is a Knight & Hale EZ-Howler. I'm not sure they make it anymore, but it's a good sounding call. Nice light reed. It's a little breathy, but the extra reed length makes controling your pitch really easy. As with any howler, throw the flex tube away, it just makes the call sound "plasticy". Use your hands to cup the bell.
I also use the Primos Hot-dog and Lil-dog from time to time. They sound pretty clean, and have great range (hot dog is LOUD), and it's nice that all 3 have very distinctive sounds. I can swap from a big male sound in close cover (hot dog head without bell, cupped in hand) to a juvenile challenge over long range (lil dog close range head on the bell).
I've been playing with a Crack Predator Calls Howler and a Dog Crack, but haven't found my groove with them yet. They're a much fuller sound than the "factory models", but they're a little heavier reed than I'm used to, so they take a LOT of air for me.
The nicest part about the diaphragm howlers is that they're cheap and easy, and very efficient.
I'd say what's NOT the best:
FoxPro Skyote: Really plastic, thin sound. A little too high pitched for my taste (can't make big male vocals), and it's kinda hard to go loud with (really small reed). It's a fun little call to keep in the glove box, and it DOES give a good sound if calling with a partner on a serenade, but it just can't make the big male sounds.
Mossback howlers: I don't have the High Plains Drifter, but I do have the Bounty Hunter howler, Undertaker Howler, Banshee, and Law Dog. They all take too much air, and have very heavy reeds. They sound really breathy to me, I'm guessing BECAUSE of their dual chamber design (supposed to be an upgrade, but it's a down grade in my book).
Primos Ki-Yi: Like the name says, it's great for making Ki-yi's, and as advertised, it DOES make pretty good rabbit distress vocals (I run mine open reed all the time, don't like the closed reed sound), but ultimately, it's too high pitched to make big male dog vocals. It's good for female invitation, or juvenile challenges, but it just can't go deep enough for big male sounds. Great call to own, but not a great howler.