Well, Marvin is integrated with Dropbox, and both can connect as a device to calibre -- or the calibre server, which is a cloud technically -- but they don't sync reading position with each other. Marvin can share that info to another instance of Marvin on another iOS device, but it's not available for Android. I wonder when kguil might release an Android version of Marvin -- that would certainly solve the problem, and I'm sure tons of people want it anyway... But I suppose he knows that already...
Marvin
can tell calibre your reading progress, and that can then be stored in a custom column; it has been designed to be heavily compatible with calibre, in every way you can think of, to the point where I am
almost convinced to buy an iDevice!
And Calibre Companion does an excellent job of acting like your calibre library on your Android, but doesn't actually handle the reading; it opens the books in whichever reading apps you have installed and chosen.