Hello Ronki........and welcome to the forum.
In response to your 2nd question, what I like about riichi mahjong, it would be easier to tell you what I wasn't too fond of in other styles of mahjong which led me to choose Japanese, and stay with it.
If you don't mind a long story,
http://reachmahjong.com/en/forum/viewto ... =5&t=53313
As far as which games I most often play, I've narrowed it down to just a few.
On Android and IOS, it's Pro Mahjong Kiwame:
http://reachmahjong.com/en/forum/viewto ... 18&t=53059
On the computer, it's Mahjong Tensei:
http://reachmahjong.com/en/forum/viewto ... 418#p58804
This one I play on level 3, the hardest, which brings me back down to earth whenever I start to think I know everything. It's somewhat more difficult to win, but that's one of the things I enjoy about riichi mahjong, having to think more about your hand and strategy, in addition to the game going on auto-pilot when you call riichi.
The final way I play are weekly live games with people I have taught and converted to Riichi from the Chinese game.
As for Tenho, if you are referring to Tenhou Online, I believe most everyone here are quite familiar with the site (since I am too and I'm usually the last to find out about these things).
If you need or want more info, we are friendly group here and very willing to help....and make people happy.