The Silverblack Spear is great if you are dueling at SL150 (against katanas). Be sure to equip the Old Leo Ring in case you trade.
I use Straight Swords (Varangian Sword is my favorite) against spear users.
Also, I always have a dark infused Transgressors Leather Shield (100% dark damage reduction), a magic infused Magic Shield (100% magic damage reduction), a lightning infused Sunlight Parma (100% lightning damage reduction).
Make sure you stock up on Dark Leech Troches (increases dark resistance) and small burrs (increase magic, fire, and lightning resistance).
As others have said, parrying is a great tool to counter both spears and katanas, but more specifically the back-step parry. Here is how to do it:
Back-step the first attack while blocking with your shield and the weapon will pass through you due to back-step i-frames.
Immediately press the parry button as the second attack animation starts (third for the Ice Rapier as it comes out just a little bit slower than the first two).
Press forward on the left analog stick and R1 simultaneously.
Riposte.
Note, if the weapon actually contacts your shield do not parry!
Just sell out and give in to the parry. You will lose a lot at the beginning, but you will also start to get a feel for the timing. Once that happens you will get good at the back-step parry. Also, katana and rapier users are generally very easy to bait into rolling attacks, which are the easiest attacks to parry.
I used to suck at parrying, but I sold out to it and now I parry the crap out of predictable players (some players are too good/unpredictable to risk trying it, but you will know those when they immediately adjust to punish you for the parry attempt).
Sorry about the wall of text, but I know the feels because I was there once, too.
Don't forget to try to have a little fun with it!