To me, they're kinda equal. Obito's Kamui is superior in a few aspects, such as being able to transport wherever he wants without a marking, plus he can teleport people and objects to and from a separate dimension.
However, FTG is way faster so in a battle of speed it will win; for example Minato vs. Obito/Ay. Not only that, with Kamui you have to know where you're teleporting in order to get there, but that's not necessarily true with FTG. For example, when Minato saved Kakashi and Rin, he didn't know where they were, but because Kakashi had the kunai with him, he was able to instantly teleport to where Rin and Kakashi were. The same applies to when he saved Kushina...he didn't know where Obito had taken her but he was able to save her because she had the marking embedded in her seal's formula.
