Pannier Recommendations

Hey, I was wondering if you all had any recommendations for panniers. I was planning on mainly using it for commuting (I use a leather brief case now) and relatively small grocery/store runs. It’s pretty rainy where I live so I was thinking something more waterproof. I’ve been reading the wirecutter, etc reviews but it seems kinda hard to narrow down for a first time buyer

Additionally can I get away with just one or do you really need two for balance issues?

Thanks!