I recently upgraded to a SG Tab 3, and went through the same thing. Off the bat, Aldiko and Moon+Reader had the best reviews, so I downloaded both.
Aldiko is aesthetically, nicer, save one area: page content. When I'm reading, it seems like the margins and the print, even minimized, have about 50% less text than other reader apps do. This gets annoying, b/c i'm turning the page every 25 seconds.
Moon+Reader is better about that, but still not perfect. It seems more feature rich, in terms of caliber- like I look at Aldiko as more an everyone's basic reader app, perfect for kids and people who just want the easiest thing to navigate- it's very simple in terms of interface. I'm not saying it doesn't do a lot; it does, but the package it's tied up in just doesn't do it for me. Moon+Reader seems to be less concerned with aesthetics, but it does more. If Aldiko is your kid's app, Moon+Reader is your grown up app. Aldiko is sort of... cartooney.
On a side note, someone mentioned Moon+Pro- both Aldiko and Moon+ have premium versions, and from what I understand, the only difference is that the paid versions have no adverts. Given the low cost to upgrade, I think they're more than worth it for not having distracting ads, and it's always nice to be able to support the designers in some way, for whom they are a labour of love- but if you're expecting more bells and whistles with the premium versions, you will be disappointed.
All that said, I still wasn't happy. So next I tried FB Reader. Immediately, I loved the page layout- at least 2x-3x more text per page, and it has the ability to scan my folders and find ebooks to import. Cool, except, it kept importing doubles and trying to manually import one or two newly added books to my device was a hassle. I couldn't scan, b/c it would end up adding everything a second time.
I also had a LOT of crashes- and not when I was doing anything particularly intensive. It seemed to crash a great deal while I was scrolling through the library- at which point i'd only added about 60 ebooks to- so that was a problem. It does read more than just epub, but those crashes, and a couple little bugs (not importing all the books in the ebook folder, etc.) were enough to make me move on. I will say I kept it on my tab3 for awhile, b/c I simply liked reading with it- even if I used Aldiko to manage the library aesthetically, and FB just to read stuff- but I finally gave up and deleted it, with Moon+Plus.
I started relying on Aldiko again- I tried a couple no name apps for epub, but none of them were worth mentioning. Then I found UB Reader.
UB Reader is hands down, my favorite- but oddly, I didn't read anything about it when I was researching. I downloaded the app as a fluke, just to try- but it beats out the others.
For starters, it scans my folders like FB, and it gets all of them; it NEVER (knock on wood) crashes on me, and it is both aesthetically pleasing in terms of library display and page display. It has about 3x more text per page than Aldiko or Moon+, and it lets you choose from a white background, a sepia one, or a black one (for night). This is huge to me, b/c I get migraines, and the white background kills my eyes. Sometimes though, the black background is not optimal, so the sepia is awesome.
It has every feature the others do: notes, bookmarks, highlight; adjust the text size, color is displayed well. It has a progress bar and a search feature, and you can organize your library by title, author, or recently read (Ascending and Descending). You can create additional library shelves. It has several layout options. When you turn the page, it actually looks like a page being turned, but it's smooth and quick.
It's free, so there are ads; I don't know if a pro version exists, but i'd happily pay for it. As it is though, the ads are not terribly distracting; they show at the bottom when you look at your shelves, but not while you read.
UB Reader only reads epub and DRM- this, for me, is not an issue, b/c I use Calibre and just convert everything when I edit the metadata, but I also don't buy a lot of mobi formatted books to begin with- if you were a big Kindle shopper, it might be more annoying to someone. Of course, you could just toggle between UB Reader and Kindle's app.
I think a lot of what makes it preferential is going to depend on you- initially, I was irked b/c nothing looked like the previous ereader I had, but I eventually forced myself to stop being so ornery and just learn to adjust. UB Reader isn't like my old ereader, but it does everything I want and looks good doing it. It might be different for you.
That's my two cents, anyway. I'm sure some folks far more sage than me will sound in. Hope that helps
