Which suits your particular demographic/flavour of gay?
My findings follow below
Grindr: Mostly 18-32 athletic/in shape guys. Some attitude, a lot of douchebaggery, and the admins are generally very anti-lulzy. The public photo restrictions are beginning to approach Puritan levels, as opposed to the golden days shortly after its launch where tugged-down-jockstrap shots and clearly visible outlines of cocks in overly tight jeans shots were common, and positional preference and dick sizes were clearly posted for all to see. Nowadays, the zealous admins parse things as innocuous as "NSFW" and "Ate.5in T0p" as scandalous, b&-able offenses guaranteed to make Her Majesty the Queen blush. (Anecdotal: the 8.5" reference got me a warning that I had better keep my wording "something that my mother would not be embarrassed of", lest I suffer the wrath of the b&.
On the other hand, you can send lots of n00dz and talk as slutty as you know how in private texts if that's your thing.
Jack'D: Mostly 25-45 average shape (some athletic, some really out of shape). Generally very little attitude/douchiness, more risqué public photos and profile text allowed. Admins will b& fuckheads, but seem not to be as b&hammer-happy as Grindr admins. I've seen some b&-able main profile pics and nasty-ass text persist for a while without being moderated. The downer is you only get three "public" photos and two adult photos which can be unlocked; you cannot send any photos via inter-user mails.
Scruff: Mostly bears, many of whom are muscled and under 40. Haven't had a profile there long enough to get a sense of the climate, but seems relatively un-douchey. My (limited) impression is the admins are a bit relaxed in enforcing Apple's G-rated standards, but haven't really seen anything egregiously "offensive" (yet) either.
Recon: Specific focus on BDSM/fetish community. Wider range of ages and body types. Some guys will observe leatherman and D/s protocol (or might ignore you or flame you if you do not observe a "low protocol" at the very least). As the focus is on fetish and gear, most of the profiles and photos are not overtly sexual in terms of showing skin.
Growlr: Haven't tried this. I've heard it is geared toward 30+ "Big Bears" and chubs/chub chasers mostly.
I think I've more or less outgrown Grindr (though it still has the biggest market share as a hookup/"supposd platonic buddy finder" proximity app), and seem to be liking Jack'D and Recon.