They're apples and oranges - a BD is important in almost every PvE and PvP party, an SK is a semi-offensive tank with a fairly wide arrays of spells for a melee class.
Between the two, I'd decide on the style you wish to pursue: The BD is a party support/assistant DD, the SK is a tank. In a party, that means the BD hits three to four dance buttons every slightly-more-than-two-minutes and otherwisely rightclicks the main assist, while the SK does the whole tank thing - if you're in a clan that actively uses tanks, that means a certain amount of crowd control, pacing, setting targets for the puller etc.
I agree 100% with MalineII.
I have a SK lvl 69 and i like it game play very much.
He is very good at PVP but hard to exp after lvl 60 without parts. If you have a good clan and will have big parties SK is a good choice but for a lone wolf or small clans SK sucks.
cool so im thinking blade dancer they are good in pvp to right, i played a tank in my other mmo experiance so for like 10 years now lol. i think i wanna go dps.
Honestly, you may be disappointed with bladedancer's damage dealing abilities. BD's primary role is support. If you don't want to end with "well, I'm needed in every party, everyone loves me but all I have to do is dance and I rarely kill anything" try phantom ranger instead ;) But if you want a support class with some damage dealing ability, then BD is great.
BD's are the ultimate support fighter. Everyone loves them.
SK's are the forgotten knight. No one really gives them a second thought, which means that you'll almost always be underestimated by enemies, and shunned by allies. If you like to be thoroughly engaged and truly want to master a class, the SK is not a bad place to start.
If you want to deal damage as a DE, give up on both the BD and the SK and roll either an archer (Phantom Ranger) or a nuker (Spell Howler). You won't hear many complaints from anyone who plays those classes.
I'd say go BD but I'm biased as that's my main. I totally love this character and I've got a lot of other toons. She's very popular in parties, getting one is easy. She can self buff, manages solo adequatly and can PVP reasonably well (although not with me because I'm rubbish at it :o)