Whether Android or iOS, most of the decision is going to be personal preference based on the app's UI. Free or pay, they all have free trials, so take advantage of them. In my case, my primary EFB is on an iPad, but I use a 7" Android as backup. My choice for that was Avare, mostly because it was simple (an app you expect to use very rarely should be); free in that situation is also a benefit.
This is a duplicate of a post I made to answer a similar question on a different forum:
"Best" is very subjective. Once you get past the questions of stability (good you got a brand tablet) and the basic feature set, it's mostly about which bells and whistles, and most especially "user experience" seems more intuitive to you. All of the pay-for apps have 30-day free trials. You probably want to use it and check things out.
I think I've tried all of the available ones. My primary EFB is an iPad but I have a 7" Android tablet I use as my backup (I don't use paper in the cockpit except for an emergency sticky note pad). Here's some impressions:
Naviator. Despite being in the biz since the early days of the Android tablet, it apparently still requires one to select which sectional to use rather than be seamless. That would be a non-started in my book.
Pilot. In addition to the obvious advantage of being the 800 lb gorilla, Garmin also has been very consistent in the flow of its UI (whether one happens to like it or not). Look at pictures of the Garmin touchscreen full IFR GPS like the GNS650 and you will see the same type of visual system and its iPad and Android app.
Flite Pro (yucch - Avilution was a much better name). Another early Android app, this one has a very good following, for very good reasons.
Avare. It's free and open-source. Ilike the app overall. But it's still pretty new. It was originally going to be a simple VFR app but he user base has been clamoring for more IFR features. They're coming and at a surprising pace for unpaid part time developers. I wold not pick it as my primary EFB for IFR but I would feel comfortable with it VFR.
iFlyGPS. If I were starting out today, this one would be pretty high on my list. In addition to having a pre-tablet history, I really like the flow of the program and the fact that it is both Android and iOS capable.
Fltplan Go. Free and with a history. Fltplan.com is probably the most-used IFR flight planning website for corporate and non-dispatcher Part 135 ops and has a very strong following in out GA world as well. They came out with apps a while ago and they are available for both iOS and Android. To some degree, it's a logical extension of the web site but I still have some qualms about how well it works in flight.
AvNav. Free for now, but expect it to start charging at some point. I really like the IU. A lot. But it's still in the development stage and has growing pains. Another issue is that it showed up about a year or so ago, then disappeared, then reappeared. Whether that's an indication of a decision to back off until something usable was ready or a lack of true commitment I have no idea.
There are others but these seem to be the top contenders right now
If I were you, I'd try them all!