If you're looking between those two, I'd probably say Leona, but there's some give and take. Leona is an amazing support and probably my favorite character out of any champion, but if you're looking for a learning experience in solo queue I feel she can be a bit rough. She depends alot on having good synergy with the ADC. Even if the player behind the ADC is good, his style might not mesh well with what Leona brings to a bot lane (aggression and good procs of her passive). If you're looking for an easyer solo queue ride to try and learn the role, this could prove more frustrating by being much more reliant on the ADC than your average support.

Alistar I feel is a little less dependent in this regard, a bit better of a "babysitter" type of bot support, but personally I've always found him more difficult to use. He requires better positioning and you can really mess up with his pulverize headbutt combo while you're learning him, but at the same time if you're good with him it's easier to make up for an ADC's mistakes or bad gambles, and easier for a passive ADC to follow up on Ali's setups. Like others have said though, if he's not banned, he makes a great jungler which makes it harder to take him bot, even though he does excel there.

If you cant land a Blitz q, youre gonna find it hard to land Leonas e and ult. Id say go with Alistar.

can't land a skillshot
want's to play leona
LOGIC. THIS THREAD HAS NONE.
(in short go ali)

My main support is Leona, and I run her a slightly different way.

I start Health Pendant and Ward. I use 9/21 Masteries, with Armor, Resist, Regen, and Gold for all of my masteries. I use Armor Reds, Health Regen Per Level Yellows and Quints, and MR/Level Blues. Leona is in the top 5 base regen champions of the game, top ten if you include people like Singed/Mundo/Volibear because of their mechanics. With this set up, at level 5-6 you are regening enough health that you are basically under the effects of a potion-constantly.

First back is boots and wards, and further backs are for Philo, HoG, then into a Warden's Mail/Sunfire Cape/Force of Nature as appropriate to team comps. Vs. Balanced Damage, your full build (if you ever reach it) looks like Randiun's, Lucidity Boots, Sunfire Cape, Force of Nature, Banshee's Veil, Rylai's Crystyal Scepter or Warmog's.

Yes. All the health and resists and regen. That coupled with your regen (At this point, about 60-120 health per second depending on items and mana and Baron.) makes you incredibly difficult to deal with.

To start the lane, you need an aggressive trading carry, like Ezeral, Graves, or some Sivirs, or a kill lane where a high damage bruiser is paired with you (Jax/Leona is surprisingly effective). Use your regen to bait harrass, but avoid trades until 3. Especially avoid picking fights with someone like Taric or Alistair, as you can be dead before you act again, even at full health. But against a lane with Soraka/Janna/Sona, you tend to just win.

The more harass you can bait and regen away (skills wise) the less mana they have for when you start a real fight.

As a new support? Neither.

Instead, try Taric, because he is very forgiving. With Alistar, a mistimed or mispositioned Headbutt can save an enemy champion, or get an ally killed. With Leona, a mistake with Sword of Light gets you killed.

Taric's skills are relatively low risk, and he fits into a wide variety of team comps because his ultimate increases both AD and AP of your entire team. He lets you focus on learning the functions and role of support, without also having to learn the mechanics and tempo of your particular champion.