I am guessing that you'll be an AGI sword welding Lord Knight. If this is correct then I would suggest getting the following. I've sort them by price for you so you can choose the one that is best suited for you.
Katana [4] - Cost less than 20K and can easily be upgrade to +10. You can put any cards you want into it for additional damage.
Bloody Eater [2] - 1M. Recovers 100 HP every time you kill an enemy.
Tae Goo Lyeon [2] - 2M or less. +10 Perfect Dodge. Perfect Dodge > Flee.
Muramasa [0] 25M - Good if you're going with the AGI Critical Build.
Krasnaya [3] 35M - +35 Additional attack if your base STR is above 95.
Death Guidance [2] 20M - Similar to Tae Goo Lyeon but 10 times better. 10x more expensive LOL.
Violet Fear [2] 150M - Probably the best sword for an AGI Melee knight.
Pricing and availability can be found via
http://ragnastats.com/.
Nice day.