[AnotherCat]

I use a TAB A (10.1) for most of my reading; and to set the scene all my books are epub or PDF and I buy books using PC or the tablet's web browser, not the stores' own apps.

I can't tell you what reading app is best for you but what I did was try the major ones and picked the one I liked best. For me that was PocketBook. It has an unusual menu system but I found I adapted to that with no problem and it turned out to be very efficient for me.

There are two things I place a lot of importance on. One is to have infinite control over text and background colours; I set up a parchment like colour background with black type (PocketBook claims to allow one to load images to create one's own background texture but I have never tried that). The other is to be able to control screen brightness with a simple swipe gesture for reading in differing ambient light situations from in the dark to bright light. Because LCD display contrast is far superior to that of E Ink and paper I feel it is important to be able to maximize the use of that. The other good reading apps also allow this.

Regarding communication with Calibre I most times use USB as it is straightforward and is managed by Calibre itself without need of anything else and is completely reliable. I also try to lead a simple life and just keep a selection of books on the TAB A's MMC.

For WiFi Calibre Companion seems popular but because of my other needs* I use MyPhoneExplorer (cost free and ad free, and used by me for years) which will let one upload/download/sync chosen files and folders by WiFi with a PC. It does that without any need for one to set up shares, plus it will also use USB, Bluetooth, or IP address instead of WiFi if desired - if tempted to two way sync with the Caliber database folders using it one will run into trouble with Calibre database corruption. I just transfer from the database to the TAB A and let PocketBook delete the book from the tablet when I am finished with it (it is then not shown as being on the device when next connected by USB to Calibre - if I remember correctly this and two way syncs all work safely by WiFi if using Calibre Companion.

Several file explorer apps will also allow WiFi connections but I have generally found them a bit clunky and inconvenient. There are other apps that make WiFi connections for file transfer between devices but all I am aware of are either advertisement supported or paid.

* The reason I use MyPhoneExplorer, and have done so for a number of years, is that it does many other things which I use, including sync contacts with PC (including with MSOffice Outlook), sync calendars with PC (including with MSOffice Outlook), sync notes with PC (including with MSOffice Outlook), sync SMS messages with PC and allow the PC to be used as an SMS client, will backup devices' including their system files, etc. Syncs can be from one device to the PC and then that sync with another device. These things may or may not be useful to you. If not, then the cost of Calibre Companion may be worthwhile, and may be so in any event :-).