I saw this new boat from Bratislava to Vienna. I'm going to be traveling from Bratislava to Vienna and was wondering if anyone has taken it, and whether they think it was worth it to take the boat or if I should just stick to the rail.
We took it in 2006 and found it fast,easy and generally good. There is even a cafe on board that has sandwiches.
I believe what you're referring to is the hydrofoil service. For my money a train is quicker, but a bus would be the cheapest. Either way (bus/train/boat) you'll get there about the same time.
I traveled that part of the Danube a few years ago and enjoyed the scenery although it is pretty much the same over the distance. Train travel I have taken is also pretty much the same over the miles.
I would base my decision on the difference in cost.