As a person that plays support often, many people prefer Sona, Lulu, Leona, and Taric. They all good sources of CC, and you should coordinate with your adc based on what you want your lane to be (sustain/farm lane, kill lane, etc.)
My current favorite supports are Lulu and support Zyra. Both help very well with engages (Lulu speed boost + Lulu ult on jungler, Zyra snare on enemies + ult) and are very much worth their 6300 ip price.
Thresh is actually pretty fun, but he requires some practice. Nami is pretty "okay", but I find that she needs some buffs. The cost of missing her Q is way too costly mana and cdr-wise.
And I wouldn't really consider buying Karma right now. Wait for her rework.