Bottom line is, Bladedancers are attack-based and Swordsingers are defense-based.
Bladedancers get dances that increase attack power for both patk and matk based classes. They also have quite a few offensive skills like drain health, freezing strike, hex that lowers pdef, power break that lowers patk, poison, sting (bleed-type), and an AoE poison dance. At 77+ they get silent move dance and a AoE petrify dance, and a dance that increases magical crit rate. Makes for an interesting class to play, they have high attack power and many skills, but have low CON, without HP setup they don't have much HP, but usually that isn't a problem, you can go either way or stay in the middle. BD's have to use dual-swords to dance.
Swordsingers are defensive party buffers. They have one song that increse crit rate, that everyone loves. The rest of their songs are mainly defensive, higher pdef, mdef, resistance to certain elements and attacks (BD get a couple of them as well, but not as many as SWS and not as useful overall). SWS' have few active skills beside their songs, most notable is their Entangle they use to slow other people, besides that they have heals, and cures for poison and bleed. Unlike BD's, SWS' can sing with any weapon, or even without. SWS' are very fast, with a shield they have very good defense against archers, and are fast enough to catch up to almost any class. SWS's doesn't have the offensive capabilites of a BD, but many underestimate their defensive songs that counter the BD's dances. At 77+ they get mp-regeneration song, a song that decrease re-use timer and mp-consumption, they may sound useless but are actually very good.
Both classes are a must in any top PVP group. If you like to have more skills to use actively than just singing, BD is the one for you, dual swords are also cool by default.
Personally I play a SWS as my sub-class, and find it quite fun, I like the speed and defensive characteristics of SWS. Being able to cut most magic damage almost in half just by TWO songs is pretty cool. But I sometimes miss having more active skills, hex is very useful.
another thing is if u like soloing BD is the class you might wanna go. the damage output from a BD is good enough to were your hp will always be full with vamp. also at 74 you get your dance of vamp will will pretty much make you one of the best melee solo classes out there.
From what ive heard SwS have trouble soloing but dont take it straight from me. ive only played bd not sws
Both those guys hit the nail on the head!
Getting a group as a BD is pretty easy. I remember being a lvl 45 BD and having people demand I join their Witches parties just for the crit dance I had.
One thing you need to get used to is people demanding certain dances based off of what's in you party. If you have nukers, they will demand Mystic. I remember I hit the wrong hotkey once and threw out Fire, Fury, Warrior dances and the Nukers in the party with ballistic! :)
If you ever have a SWS in your party, get ready for more dance/song micromanagement. Dance once, wait for their two or three songs, then bust out a last dance (or some variation of that).
I haven't messed with tattoos much. I have a +2 Str -2 Con.
Oh... there are more BDs out there than SWS it seems.
Pure solo play I'd say the BD would be best. But with VR and prophet buffs, any melee can solo just about nonstop on the right mobs.
SWS have the advantage of a Holy weapon toggle, that increase their damage about 20-25% against undeads, useful if there is no buffer with Holy weapon. Just thought I'd mention it, since I like the toggle :)