Pyros has good advice, you might also consider taking Ice Block at 13 over the auto rejuv, you can block during Tranq and become immune while still pushing Tranq out (nothing interupts tranq except you dying, this just makes you invuln while you do it) which allows you to position dangerously for your team and anchor a fight point. It might also fuck you if everyone runs away or somehow gets wiped with Tranq up but it is something you see more of at higher mmr.
That can be good if you play with kinda better players yeah, I'm still leveling though and in quick matches, your team will absolutely try to find every way possible to run out of your tranquility, so I find being able to move around is good. And I really like the auto regrowth. But yeah there's a bunch of levels you can pick other stuff than what I mentionned, that's just my general solo support build, I get full support shit and just run around healing people, works well. You can get the bigger stronger root, mule, the better moonfires for pew pew and stuff like that too, quite a bit of flexibility.
Out of all the supports I've played, I prefer Malfurion by a fair margin. I liked Tyrande too but picking her in quickmatch means you're losing like half of them when you're matched against a "real" healer with your shitty healing. I think what I like about Malfurion is the roots though, not the healing. Healing is adequate, but so is healing for other supports, however I feel when I played Reghar, Lili or Brightwing, you lack some good disables. Brightwing has polymorph which is great against assassins but it's obviously single target and I find his healing output pretty shit until you get the talent to proc your passive every cast.
The problem of how they've designed supports in this game though is that if you don't have the healing output of the better supports, you're shit unless you have 2 healers. That's fairly poor design. In LoL they had to heavily nerf Soraka at some point because her healing was too good too, and in Dota the healing is all around pretty shit and is more a sustain mechanic than an actual healing mechanic(you heal up after the fights or to slightly extend your lifes during fights, lengthy coolodwns and low value healing). Good supports are more like controlling/buffing heroes, rather than healing. So healing output becomes a utility rather than a necessity, something that's weighted against control/enhancing abilities. It's similar to the 2nd healer in a 2 healer setup I think, where you'll more often pick a hero that does more than just healing(Tassadar, Tyrande or just another Specialist instead).