When I started Photo Tour Brugge in 2012, I started with Android devices since the iPad was out of my budget range. First a Galaxy Tab 10 opened my options to mobile shooting (followed in time by 4 more devices including the 1st Galaxy Note, both Nexus 7 models, and a Nexus 10), and frankly from the start I found I had nothing to feel jealous about outside of Apple's garden.
While camera quality in the Android system can vary widely (the Samsung tablets had quite nice cameras, the Nexus range acceptable to painful), I found a good camera and some of these apps delivered quite pleasing and usable results, screens or small-ish prints. Funnily enough, I've been trying out iPads this year to give both sides fair consideration (and let's be honest Apple is easier to use and has consistently superior hardware) and still prefer Android apps, especially Quickpic for viewing galleries.
So, I'm just going to troll out and say it: I think Android beats the crap out of iOS for photography, hands down. While every app I listed on my Great iOS Apps for Photography (2015) post is genuinely awesome, in my opinion a lot of those apps are just not as interesting or flexible as Android. By the way, did you know that RAW shooting is currently Android-only? Pity, especially considering that iDevices have suave little cameras.
But hey, it's all down to taste, mine is split between the two but with a heavy lean to 'Droid. These apps are why...
Taking Photos
Vignette - My hands-down favorite app for taking photos, Vignette is a feature-soaked way to give your Droid camera some serious power and usability options. Particularly love the extensive (and heavily customizable!) effects and control options, and of course since this is a power app you can save that AND the original photo easily. Highly recommended.
Dslr Camera and/or Camera FV-5 - Reaching for the goal of emulating a "typical" camera with options, both Dslr Camera and Camera FV-5 offer you the usual DSLR range of features (EV, bracketing, white balance control among others) that'll open as much of your Droid camera as possible on options.
Editing Photos
Adobe Lightroom - Adobe - A major player in the photo editing game, Adobe released this app to let you synchronize your home computer based Lightroom collections (groups of photos) so you can do a hearty range of edits on the go via your mobile device. As of October 2015, Lightroom is now available without needing a Creative Cloud subscription, interesting!!!
Snapseed - Google - A powerful (and free) photo editor so good that Google bought the company! Thankfully getting gobbled by the big G actually led to this app just getting better and better, check it out for near-photoshop levels of editing options.
Photo Editor - Aviary - Another powerful photo editor (this one so good that Adobe bought it up), Aviary is comparable to Snapseed for the range of features on hand. Optional extra filters available via in-app purchase, thankfully not required to make this app a must.
Pixlr-o-matic - Autodesk Inc. - More suited for adding an overall effect in a few clicks, this app is superb for on-the-go edits without bogging you down in options in customization. Enjoy the limits, if the effect really grabs you feel free to work it out properly on your favorite photo editor.
Photo Galleries
QuickPic - I have only one suggestion for serious photo gallery viewing, and it's Quickpic. Why? Well, since quickpic offers every option in the book from viewing to customizing to connecting to accounts to hidden and/or secure folder management... There is simply no competition, yes even on iOS.
Honorable mention: Google Photos - Google's default app for viewing your photos is actually quite good lately, especially if you're looking for cross-device or public sharing like Apple's iCloud service offers.
Supremely Useful Photo-Related
Sun Surveyor - Adam Ratana - This is my go-to app to find out where the sun is going to be, so many options it would be scary if the interface wasn't so easy to use! Use the compass, map, Street View or even fire up the camera and see where the sun and moon are going to be.
Nikon Lenses / Canon Lenses - If you partake of one of these brands for your changeable lens camera needs, this app helps you by listing every lens from the respective manufacturer. Not only that, because a list is handy but info is handier: Choose a lens to see a healthy list of links of reviews from trustworthy sources!
CamRanger: Wireless DSLR Camera Control - CamRanger - A beast of an app (and this one requires a hardware purchase), Cam Ranger lets you use your iDevice to control your Canon or Nikon Dslr, pretty damn cool if you ask me!
Easy Release Model Release App - ApplicationGap - If you're a working photographer you might well know this app, designed to simplify the legal side of taking photos as far as written consent to publish the content of your photo if the face (or even place) is owned by someone you need to sign off on things. If you don't, just download this app and have it ready, you never know!
Postscript: Some of this list is the same as the iOS apps listing (here). Some of these are coded for both ecosystems, I'm luckier than them that I can copy and paste instead of another coding language.Q