Since a lot of people like Pleco, here's what they say about which device to use.
http://www.pleco.com/support.htmlShould I choose iOS or Android?
The depth of feeling on both sides of this debate is such that we don’t want to even hint that we might think one platform is superior in general to the other one. However, for what it’s worth we can state objectively that our iOS sales are roughly 4x our Android sales, and that those numbers appear to be fairly typical among other mobile app developers - we have lots of users on Android, but the bulk of our revenue comes from iOS. So we tend to spend a bit more time on iOS than on Android development because of that.
Our iOS version also has a few more features than our Android version does, though this is more due to technical considerations than any favoring of one platform or the other. iOS includes built-in support for decoding PDF files while Android does not, so our document reader on iOS can reader PDFs and our document reader on Android can't; likewise for Word/RTF documents. iOS also has a better and more consistent font rendering engine, so we're able to do much nicer things with typography on iOS than we can currently do on Android. (both the PDF and the typography gap are set to narrow in the new Android L, though)
So if you simply want to choose the platform that has the best version of Pleco, at the present time that platform is iOS. And absent a dramatic shift in where our sales come from, that seems unlikely to change anytime soon.
Which device should I buy?
iOS: if you're getting a new device, we think the $100 premium for an iPhone 5S / Retina iPad Mini over an iPhone 5C / non-Retina iPad Mini is more than worth it for the improved specifications, particularly after we upgrade our OCR engine to take advantage of 64-bit processors. The newest iPod Touch is a pretty good value and should also run Pleco fine if you want a pocket-sized non-phone device.
Among used iOS devices, we're about to start requiring iOS version 7 as a minimum, and plan to be fairly aggressive in requiring iOS 8 early next year, so we wouldn't get anything older than an iPhone 4S, an iPad 2 or the newest (5th-generation) iPod Touch. We would also recommend that you avoid the iPad 3, since its processor was really too slow to drive its Retina Display and as a consequence it's just about the slowest device for running Pleco that you can get; the iPad 2 and iPad 4 are both better choices.
Android: for Android, we recommend that you get one of Google's Nexus phones / tablets; they're a very good value for the features they include, and because they're from Google they always run the latest, best, most stable version of Android you can get. Devices from other manufacturers like Samsung tend to be overpriced and to add a lot of extra customizations that only serve to make Android worse, on top of which it's rare for them to receive operating system updates as quickly as Google's own devices do. At this point in the evolution of mobile devices, having the newest software matters much more than having the newest hardware, and the best way to make sure that you get access to that with Android is to buy a Nexus.