I stayed at Casa di Sara, the sister pension of the Ca' San Trovaso, in 2009. TC has outlined the pros and cons of the three options well.
I chose option 3. I bought a vaporetto pass, and in 2009 it included the bus number 5 from the airport to Piazzale Roma (this now costs a few euros extra when added to the pass). I then took the vaporetto to the Zattere stop and walked. It does require going up and down some bridges. Take vaporetto 5.1, which goes counter-clockwise around the island.
Here are their directions, copied from the e-mail they sent me in 2009 (even though I stayed at Casa di Sara, I still checked in at Ca' San Trovaso):
"Get off at Zattere;exit left,cross 1 bridge ( "PonteLongo") and after 100 meters,on your right, you will see a big white palace with flags,turn right,walk "Calle Trevisan", cross 2 little bridges;immediatly on your right we are there,yellow house,Calle Pometti, door #1351."
These directions were perfect, and very handy when jet-lagged!