I've been using Spiral Heat for quite a while now. Pretty good raw (345), and seems like a lot of things are weak to fire in this game. However, I just made the Tusk Lance+. Has less raw, but the 40% affinity more than compensates. Also has a good amount of element on it. As said, Undertaker is pretty beast as well if you can make it.
Just landed a undertaker offline myself on my last Agnaktor run. I feel really lucky but I was also a little sad its attack power matches my Babel Spear, but has 250 dragon on top of that. Well, I lost a slot and 16 Def, but its got its use for that still I guess. I 'll just swap them when the Dragon is worth using.
So on that note of the differences I would recommend the Babel Spear if you can't land an Undertaker.