I use FBReader. It's free and does the job when I need to open an epub on my laptop, but honestly I put everything on my tablet to actually read it.

Scale 1 to 10, 10 for the best, how was it?

Calibre, but i don't read on the pc if i can help it. Kindle device for me, or my tablet.

[jjjaaazzz]

None. I convert to mobi for Kindle

[dissipate]

Adobe Digital Editions mostly in the past, but in the last 2 years it has been slowing down and hanging a lot am using Calibre 20% of the time now.

On the PC, I used to use the C language version of FBReader, which handles ePub, Mobi, FB2 and other things. It does not handle DRM, but I don't get stuff with DRM and don't care. (I use the Java port on Android.) These days, I use SumatraPDF, which renders ePub and Mobi as well as PDF, and does well enough for my purposes.

I have the Adobe Digital Editions app installed, but seldom use it.

In Firefox, I looked at ePubReader and passed. It insisted on creating a local library of ePub files that it would store in the Firefox profile, with no option to place it elsewhere. (I was keeping my Firefox profile on a ramdisk, and space was an issue.) I currently use Lucifox (https://addons.mozilla.org/en-US/firefox/addon/lucifox/?src=search) which doesn't have those annoyances.

Calibre's built in reader works well, but invoking Calibre just to read an eBook is more trouble that I care to take. I use Calibre to maintain my eBook library and do format conversions where required, and the built-in reader is mostly a visual check on how things will look. Most actual reading is on my Android tablet.

The main things I might actually read on the PC are PDFs. They are a poor fit for small screen devices, and while I have them in my Calibre library, I use a Virtual Library that only displays ePub when I'm selecting books to transfer to the device.

[Fizban]

Calibre's built in reader works well, but invoking Calibre just to read an eBook is more trouble that I care to take. I use Calibre to maintain my eBook library and do format conversions where required, and the built-in reader is mostly a visual check on how things will look. Most actual reading is on my Android tablet.

No need to actually run the main program all the time - it's actually possible to use the built-in reader as a standalone, which is what I do.

You right-click on an epub and/or mobi and choose Open With -> Choose Default Program. If you don't see "The Calibre e-book viewer" as a recommended option, then choose Browse and make your way to the directory where you installed Calibre and choose "ebook-viewer.exe". Make sure that the option is checked to always open that filetype with that program and you're good to go.

I have it set so all epub and mobi files open with it so I don't have to hassle with Kindle for PC or Digital Editions, Calibre main program, etc until I really need them.

[gorkevv]

I use Sumatra pdf- minimalist and straight to the point.

iBooks or Adobe Digital Editions ... I find Calibre good ... but time consuming to load ... so I no longer use it ...

It looks like I'm the only one still using Sony Reader. It gives me all kinds of problems, though, so thanks for all the suggestions in this thread! I don't like Calibre's reader for some reason, but I'm going to try ADE.