I am a lv 30 player on Taiwan server and play with my friends as a team
as others like to play other roles, support is left to me all the time
(except someone want to try support, then i switch role with him)

my friends tend to take normal games really serious
one slight mistake can make them start moaning about how should i do in the next few games
especially when i am supporting the most skilled one in bot lane
the experience and skill level difference sometimes make me hard to catch up with him

i don't want to blame anyone as i AM low skilled and suck at some aspects in game
lately i find that alistar is kind of not suiting me
i played him for nearly a whole month without playing other champ
and i just can't fully excel his utility for my team
also often screw up team fights with his Q and W

the supports i am good at are soraka and sona (planing on buying leona)
but whenever i choose the girls my teammates yelled at me
saying they are pretty weak in any aspects and shouldn't be used in my life time
this leaves me a question

a tanky support vs a poke support / heal support
which one is better and why?

Depends. Who's your carry? If you're doing draft and/or ranked, what are you going against? Do you want a kill lane, a poke lane, or a farm lane?

Alistar, Blitz, Taric, and Leona are typically good for kill lanes.

Janna, Sona, Lulu, and Nunu are typically good for poke lanes.

Soraka is the best for a farm lane.

That being said, both Alistar and Taric can do well in a farm lane since they have a heal. Personally, I think an Ezreal/Sona lane is a poke lane that turns into a kill lane since they have so much poke between the two of them. So, nothing I listed above is set in stone.

Typically, the more burst a carry has the better off they do in a kill lane. For example, Ashe and Caitlyn tend to do better in a farm lane while Graves and Ezreal are strong in a kill lane.

You also need to consider what you're up against. Taking Soraka against Blitz is asking for disaster. You'd be much better off with Taric, Alistar, Leona, or Janna if you know how to use her. Nunu, on the other hand, loses hard to Soraka. Her silence has a longer range than his snowball. Every time he steps up to snowball, she can silence which leaves him over extended and helpless.

Long story short, there's no one best answer. Your best bet is to learn which supports compliment which carries, which supports counter which support, and which supports fit best on your team overall. If neither your top lane nor your jungler are tanky, you probably want a tank support. If you already have 2 tanks, though, Soraka can invaluable to the team.

Finally, don't listen to anyone who says Soraka and Sona are garbage. Soraka's considered the top support with Janna for a reason. And when played well, Sona is a great asset on a team too.

I used to play Soraka a ton, but I've found her to be absolutely worthless after the laning phase lately. She's just kind of "there".

If your teammates think that Sona is worthless, then they probably suck much worse than you do. Especially after recent buffs.

It's all about Bot-lane synergy. You need to pick a support that matches your ADC well (though sometimes a support can be used for counterpicking, like how Alistar can counter Blitz).

For example:
Graves, Corki, and Ez are kill-lane/burst ADC's that fit well with CC supports like Ali, Taric, Blitz, Leona. These are the most popular combos for bot-lane in the current meta.

My reccomendation would be to learn Taric and Janna. Taric is probably the top support right now (he IS the most popular according to the statistics), at least when played with an ADC like those listed above. Janna comes in at a close second, but fits better with a poke lane like Ashe or Cait.