It's really hard for me to recommend one version over the other because I'm still a bit nostalgic for the original. War of the Lions really adds a lot to make it a more appealing package, and when you put it all in writing it's hard to overlook that it's probably the best version of the game available. While both games are mechanically the same, WOTL removes a few exploits (such as one that gives you 9999 Job Points or one where you can duplicate weapons), includes two new classes, a guest appearance from Balthier, and I believe it has some sort of multiplayer as well. Not to mention that the remade cutscenes are absolutely gorgeous, and the game was completely retranslated to give it a more medieval feel like FFXII.
I feel like for most people, it's really come down to which translation they like the most. Tactics had the same problem that many JRPGs of the time had, where some phrases were translated out of context or don't make much sense. Likewise, I think that War of the Lions comes across as a bit to "wordy" at times, whereas a lot of times the original Tactics actually manages to be more succinct in its delivery. The best way I can describe this is by mentioning one of my favorite quotes from the original, which is directed at some thieves during the first fully controlled battle. The original line was
"Silence! Surrender, or die in obscurity!"
In the WOTL, the line is
"Lay down your arms or die clutching them! None will mourn your passing."
Other than that, you're in for an amazing game if you choose to give it a chance. The battle system is as layered and complex as it is rewarding, and the story is surprisingly the most mature that a Final Fantasy title has ever reached. It also features one of my favorite female knights in the franchise and what is arguably the most badass version of Cid (or second most badass, you really can't make a good case against Cid Highwind). Just make sure that you keep multiple saves and learn the Auto-Potion and counterattack abilities if you choose to play the original, because there's nothing as soul-crushingly depressing as having to delete a 14 hour save file because of how impossible a certain boss fight becomes (which I believe was also altered for WotL, but is probably still hard as hell).