Everything you should know about TRAPPIST-1 exoplanets

I've now heard 3 different causes for Io's surface getting energy from tidal forces. 1) Io's orbit is elliptical so the tidal force changes in intensity between when Io is closest to Jupiter versus when it is farthest from Jupiter. 2) Io's orbit is elliptical so it speeds up and slows down as it goes around Jupiter. Angular momentum causes Io to rotate at a constant rate. The difference between these two rates means that the tidal force vector points at Io at different angles throughout its orbit. 3) and now there is something to do with the orbital resonances with Europa? I would like to know more about this 3rd option. Also, between 1) and 2) which is more important? i.e. does the tidal force vector changing magnitude have more or less influence than the tidal force vector changing direction (relative to Io)?