I've been personally playing WoW since a few months after release and one of my favorite classes is definitely the Paladin.
Being able to Heal, DPS, Wear Place and take on many different roles in the game always made me feel useful in groups and powerful when solo playing.
I've leveled several paladins, in fact my first 60 was a Paladin.
Many changes have happened to all the classes in WOW over the years, there's been Nerfs and buffs, sometimes it seemed like they were doing this every single patch.
Since the release of WOTLK Paladins got quiet a bit of love in my opinion especially in the DPS area were once the term "DPS" and Pally were used in the same sentence a "LOL" would be nessacary.
So, you have a Paladin or maybe you're deciding to roll one.
There's basically just one question you have to ask when deciding what main talent tree to go down.
Will you be mainly playing with a Group or Solo? If you're playing in a group you can go down any tree, just decide if you want to heal and go Holy, Tank and go Protection or DPS and go retribution.
If you are going to mainly Solo play then without a question you should go Retribution.
You will level the fastest.
When leveling it comes down to how fast you can kill things to get XP to turnin quests, and Retribution will let you kill the fastest, therefore completing more quests faster.
Also Retribution is great for Battlegrounds so when you want to take a break from leveling and jump into a BG you can and handle your own.