Well both are useful, with tailoring you can support yourself with armor, with engineer/mining you can make useful dodads and some good goggles for casters. I am an engineer miner.
I've enjoyed engineering, it's very differant. Not too hard, and you have that "excentric" style. Not everyone can summon a pet dragon or shrink you, spend forever underwater or jump from very highplaces and survive. I'm a rogue, so all these gadgets fit the kind of character I wanted to be.
As for tailoring. To answer your question, yes and no. Tailoring requires no gathering becus it's droped off mobs. Huminoid types, or undead humanoid. Basicly you're taking thier cloths and gathering that way lol. It does need other things like leather or a potion sometimes, but every proffesion does that on some items.
You can get the materials easily enough if your of apropriate lvl for the type of material. Low lvls linen, then wool to silk to mageweave etc. Only difficulty is if youre too low and your skill needs material that you cant kill for. There's always the AH but that normaly runs a pretty penny.
Not uncommon is the coupling of enchanting and tailoring. Since both are stand alone proffesions, you can make cloths in tailoring, break em down for enchanting, enchant your cloths you made for yourself. Etc. As you get better at enchanting it's very profitable by selling enchantments to players. This helps with tailoring aswell since you can afford to buy the silk or whatnot.
I hope this helps you somehow ^_^