With the increasing ease of access to hi-resolution tablets, reading electronic editions of comics is getting easier. In the last few months I've taken to collecting a lot of back-issue trade paperbacks on both the Marvel and DC lineups, as well as using the medium to experiment with third party books (Cyberforce, Savage Sword, Robyn Hood and others to name a few). As a result...I have a few bits of advice and direction to help out those curious about the choices available.
First off: Choice of tablet is pretty important. Make sure you get a hi resolution tablet, and make sure it's noted for how decent the resolution is. The screen size can have an impact as well. For example, my reader of choice is my Nook HD+ which at 8.9 inches with a 1920X1280 resolution screen is fantastic for reading comics. I was enjoying my Asus Transformer Infinity 700T which has a bigger 10 inch screen but roughly the same resolution, and the pairing doesn't work so well; things which are sharp and clear on the Nook HD+ can be muddy on the Asus. So....do your research carefully, but of the various tablets I've tried the Nook HD+ is the best size and resolution for me. If you have youthful eyes and don't mind tiny print you might get away with using a Nexus 7, too.
Second: choice of app is also important. Right now you can buy comics through a variety of mediums. I haven't explored Comixology or Kobo yet, but I have purchased comics on the Google Play, Nook, Kindle and Marvel Comic store apps. Here's my quick run-down on each:
Google's comics are hi-res and larger size files. The store is the one you'll be familiar with on Android platforms. There's nothing wrong with Google Play, and it was my default venue for a while, but three problems crop up with it: first, it's very slow to load books. Put them in queue and wait a while. Get too many downloads going and wait a long, long while. Second, not a lot of customization on how to view your library of content. You can't hide former reads, only uninstall and note what's got the little blue circle to indicate what is and isn't loaded. Third and of consequence mostly to Marvel readers, Google's editions of Marvel books are not synchronized to show pages correctly...when you have a double-page splash you can't see both pages at once by turning the tablet on its side, nor does it "shrink" them for viewing at the same time. Big problem.
Google's prices are fairly competitive. Some of their library is a bit pricey compared to the competition, but they mark sales better. Searching for stuff is a weird experience....for a Google product you'd expect their store to show you all the related content you are looking for a bit better. Finally, Google Play does have plenty of Trade editions and is getting lots of DC single issues, too....but no single issues for Marvel.
The Marvel Comics app is the best place to find Marvel offerings. They seem to keep some issues and editions in reserve for their store only, and it's the only place to find single issues as well. Marvel's also got a promotional thing in virtually all of their print books where you can get a code that will give you access to an electronic edition of the print book, and sometimes this code includes other free comics or TPBs as well. The downside of the codes is that you pay $4 for a book to get a code for the comic you just read....useful for future reading, I suppose. The stickies that hide the code are also prone to malfunction...about one in five tends to come off wrong, and then it's a guessing game as to what the code actually was supposed to be. Still, it's a cool perk if you like the idea of having e-copies for posterity.
The store itself is a great reader, and includes a feature which lets you tap to highlight specific panels, which works a bit better than the Kindle version of the same (in my opinion) but is just as useless, at least for how I like to read comics (I really prefer a full-page view). Unlike Google Play and Kindle, most of the Marvel comics in the app will correctly display double-page spreads for reading.
The main problem with the Marvel store is price. Most TPBs are discounted, but all single issues are priced at the same cost as a print issue, and rarely seem to get discounted in price. Still, hard to beat as a place to find the occasional issue you can't locate anywhere else.
A second much more serious issue if you travel a lot and are away from wi-fi is that the Marvel Comics app will not work unless you are able to log in remotely. For this reason alone I don't buy on the Marvel Comics store unless I have no other choice. Apparently it's never occurred to Marvel that the main time people read content on a tablet is likely when they are not near a computer, which means that they likely aren't near a convenient wi-fi hotspot. If your circumstances are such that you never find yourself away from a connection this won't be a problem for you, though. For me...it means anything I have on the Marvel Comics app probably isn't accessible when I go on vacation.
The Kindle app is friendly to use and has a wide selection, but its files load fast for a reason: they are lower-resolution smaller files, and show poor quality compared to the other stores I discuss here. Marvel comics also have a "read" problem with double page spreads, and the panel-zoom is a pain to use in my experience. I disliked the Kindle app as a comic reader enough that after trying out Wonder Woman, Hawkman, Five Ghosts, New Avengers and a couple others I gave up and moved on. Even the occasional ridiculous sales prices Kindle offers aren't worth the savings....you will find these unpleasant to read once you're used to the higher quality of the other store apps.
I'm a Nook fan, but I don't think that overly influences my buying decisions as much as does the fact that their reader rather nicely displays hi-res files, load quickly, is easy to navigate, and also correctly shows double-page splash scenes in all cases I've tried so far. They occasionally have sales, and for some reason I've found books on Nook that aren't on Google Play (they might be on Google Play, but the search engine over there is shady at times). All of the Nook comics I've loaded to date are very nice and clear hi-res copies, too.
Nook's main problem is price....you'll typically pay 50 cents to a dollar more for many titles on their store than Kindle, though they tend to be comparable to Google Play more often than not. As a result, if price is a big issue, I'd suggest Google Play (which will have more discounts over time), but if ease of management for your library as well as good download speeds for bigger hi-res files counts, then stick with Nook. Still, if you stick with Nook then you can avoid supporting the predatory nature of Amazon and stave off the inevitable collapse of the publishing industry into Amazon's hole of mediocrity a little longer.
It's possible the Kindle works best on the Amazon tablets. It's likely that if Google Play resvises the Google Books app then it will bump up in my estimation...and if you just want Marvel comics then you really do need the Marvel Comics app. But from my experience to date, the Nook store gives you the best and speediest reading experience.