Engineering, enchanting, and alchemy are currently the three best crafting professions for most paladins.
The easiest approach by far is to work on two gathering professions until lvl 70, make 5k gold for your epic flyer, then make another 5k gold and max out the crafting profession of your choice in a day or two.
If you already have a main character who's flush with gold who can fund your pally's levelling adventures, that approach isn't so important. In this case, you might want to level engineering as you level your character, because you can take advantage of bombs and other ranged goodies to make up for an early deficiency.
As the pally FAQ says, enchanting gives your character access to ring enchants, which are nice. As the tradeskills FAQs describe in detail, a skilled enchanter can make insane amounts of gold by disenchanting green/blue items while they level (bad enchanters, on the other hand, tend to lose a lot of gold because they're idiots).
In general you should not skip gathering professions entirely. This is hard for a lot of people to understand, but the value of raw materials in the World of Warcraft is almost always greater than the value of the finished product made from those mats. The fel iron needed to make Tsarducci's armor set, for example, will cost roughly three times the amount that blacksmiths sell the armor for on the Auction House. Being able to mine your own ore or pick your own herbs creates a pleasant illusion that you're not really squandering huge piles of gold to level your chosen craft.
You don't have to rush into choosing a crafting profession. You can wait until you have more insight into the options, and gather in the meantime!