Re: Roland or Yamaha?
They use different technologies.
Yes, Yamaha kits' sounds are based on sampled acoustic kits. The pads are generally larger than Roland and like all their gear - they are a very good manufacturer. All the ones I've seen are rubber, which is fine. The Yamaha kits tend to be larger than Roland and so if portability is an issue you may prefer Roland.
The Roland kits drum brain takes electronic signals from the triggers during play, and uses built-in sounds and a variety of other electronic technologies to recreate the sound of authentic drums, recreate or synthesize percussion instruments of all types, and to signal other MIDI-capable gear to perform various electronic tasks. This means that any drum/percussion instrument can be emulated. There are websites dedicated to supply e-kits for download to the Roland brains. This could be Bonham's kit from Led Zep II etc etc.
The better Roland kits also use mesh heads, which some prefer to rubber pads. The TD9 you mention has the ability to change the size of the various drums and so you can have a 1" up to a 20" hihat for example. Experimentation can be a lot of fun.
All of which means nothing if you haven't tried either. So give them both a whirl.
I'm a big fan of e-kits but you will find a depressing high number of forum-lurkers who spend a good portion of their time putting them down. Just ignore them, they may grow up one day and accept that other people have opinions too.