My wife and I spent at Appiani36 2 nights and it was a very good choice.
We came to Treviso airport from London at about 22.00 when the only way to get to Treviso city was to hire the taxi. It costed us EUR 14 to the Appiani36 (center of town) but you may pay even twice less if you share the taxi with somebody else.
Actually it is only 7 minutes drive from the airport.
We took 1 room at Appiani36 and it was spacy and clean. Breafast was nice and Federico's (owner of the B&B) advises were highly useful.
Treviso train station is about 20 minutes walk from Appiani36 but better not to rush to Venice - I recommend you to spend at least 2 hours to discover Treviso.
Train takes you to Venice just for 20 minutes (return ticket costs EUR 4.50) and you may return back even in midnight without risk to be late to the last train.
General impression: Excellent place to stay
