Spear is better due to speed. However, Sword has proven to be equally versatile and fun. Honestly, it's up to you. Both are very OP in PvP so that's not even a factor. . .
Let me put it to you this way - do you like fast hits that keep you in one place for the most part OR do you like slightly slower but stronger hits that move you forward (basically attack while moving which is very helpful when you KB lots). Also, doing dual is kind of a waste IMO. The 5th tier stopped being special A LONG TIME AGO. You should just spend that 30m-40m you'd spend on SS5 coins on super puzzles/enchantment remedy/tears to make yourself a godly Coliseum weapon with oodles of yummy Accuracy, Min Damage, and Max Damage~
IMO: I'd go for Swords. Swords are fackin' awesome.
Or, you know, just play a Highlander which is x5 awesome.
"He who fights and runs away, lives to fight another day!"