Black Knight halberd , Black Knight problems

[Dracus]

Hello, I'm new here and I have a Question about Dark Souls.
First my info: SL 21 STH 16 DEX 16 END 16 I use a +2 claymore .
I just defeated the Black Knights in Undead Burg and Darkroot Basin, the latter dropped me his halberd which requires 32 STH and 18 DEX .
I saved around 20000 souls and I still haven't been to the Lower Burg, Beaten the Hydra or cleared the depths; when I'm done with those tasks I should have around 70000 souls, and that's about enough to two-handedly wield the halberd(to single-handedly do it I need 108918 souls).
So should I invest my souls in STH and DEX till I can two-hand it or just keep upgrading the claymore( I have enough to get it to +8)?
Also the Black Knight in the Parish, I can parry all his attack(that's how I kill his two compatriots earlier) except an attack where he leans down and do a spin that sends me flying; so any advice about how to deal with him.
Also, I keep seeing videos of players strafing around BKs and getting back stabs, yet when I try it the knights just keep spinning around along with me so I always face them forward (my Equip Load is under 25% thanks to Havel so it's not about my speed) and when I think I'm not in rang for their attacks they somehow end up hitting me.
Any advice is appreciated, and thanks in advance.
Update: Should I try to get the BK's great sword? is it better then the halberd?

 

[XMark]

I would recommend getting the levels up to be able to 1-hand it. My first play through the game, I had the black knight halberd all the way to the end of the game. It does ridiculously huge amounts of damage and has a very useful moveset.

 

[Dracus]

I should mention I already have enough twinkling titanite to get it to +3

 

[default]

Always get enough strength to use your weapon of choice single-handed. Shields are bloody important, and with the halberd it changes up your moveset quite a lot. Flexibility is always important, and you can easily get that amount of strength you need.

The Black Knight Sword is pretty good. I used it for a while myself in PvP but its moveset is pretty substandard. Never try to use the heavy attacks, they leave you wide open and asking for it. The Black Knight Greatsword is a bit better in my opinion, plus it has some really sweet heavy attacks. It's very satisfying landing that two-handed uppercut on an opponent in PvP and watching them rocket up into the air.