This depends on what do you want from your control wizard. If you want to completely pin down an enemy, one Frost Jolt wouldn't be enough against Humans and Elves. If you just want to slow him down, to let your warriors catch him and finish him, then you may prefer Staff of Winter (especially if you have an Elf Warrior). If you're playing 2+ wizards, then you may just finish your enemy with Frost Jolts + Paths of Knives, but I still suspect that freezing him completely and spamming Fire Wall/Spikes for him would be much more reliable. Cone of Cold is good just for completely pinning your opponent, that's why I'm playing two Frosty Staves. Cone + Jolt block almost everything, even Nimble Strikes, for 2 turns. I may try changing one staff to Staff of Winter though since I have Larkin's Orb and Xemu's Crown But Sub-Zero would be really great.