Personally, I never saw the point of getting UC as it doesn't really help in training. As long as you use elemental melee, your fine. And the MP cost isn't very effective anyway. 25 TMs may seem like a lot now, but once you hit 3rd job you need every TM point you can get. If you're going to get UC+Counter (UC is useless w/out counter imo), plan on skipping out on Quad/Tetra until you see UC/Counter show up in the skill build.
The reason you only choose one or the other is because you want to save points for Adrenaline, and there really isn't any point in bossing until level 180, and by then you should have the skills needed to take on Count, unless of course you over-party quest and kill your TM.
I personally didn't try the trials with just UC+Counter, but imho I think Tetra is a wiser choice.
+ Tetra has a 7s cooldown, UC has 11s
+ Tetra is overall a stronger attack (100k+ vs. 40k~70k in Beach Field 4 for me)