This is hard to say 'cause he was a potion genius , plus his DADA skills mesmerize me. What can I say? He was the greatest wizard of his time

I'm choosing DADA. It's something he was very interested in and passionate about since he was a child. Much more so than Potions. Makes me wonder if there was a DADA textbook covered with new spells, just like his potions book.

Probably better at DADA but there's not much to go on with the limited information we have on his skills. Though Dumbledore does seem to consult Snape with matters pertaining to the dark arts.

My opinion only, canon doesn't specify.

So, Potions seems to be the only thing that Severus had a true interest in from childhood. He only seemed to turn more fully to the Dark Arts after the disagreement with Lily.

And, I feel that his desire for the DADA position year after year was wanting to truly teach the art, not keep watching lackluster professor after professor come and fail to teach the class to its full potential.

So, I feel Potions was his true art, his genuis. He would have been an excellent DADA professor, better than all that have every held the position. And, that, is the reason that he wanted the job. He knew he would be better than each professor that ever was hired by Dumbledore.

Both he is good at everything.

Potions' Master....DADA Professor and Deatheater.....hymmmm......