I'm making something with Broccoli and cheddar, what would be a good herb to use? Dill? Oregano? Something else??

I wouldn't bother with anything: Broccoli and cheddar are both big, punchy flavors and I personally think any herb would just be sort of a weird distraction.

Instead? Bacon.

I would use thyme, and a tiny bit of nutmeg and/or cayenne would also be good (in addition to the thyme). You could use fresh thyme if you have it, or dried thyme (use less if it is dried). And/or a bit of dry mustard.

Nutmeg and parsley. Both broccoli and cheddar are full of flavor so they really don't need much help. Bay leaf wouldn't hurt if there is any braising involved, or a bechamel to infuse. ;o)

Sumac could be interesting. I like it with broccoli and I put into very cheddary omelets as well.

There are very few herbs that pair well with broccoli. Tarragon is one. But if the broccoli and cheese are the stars I would be inclined to go with a spice instead , perhaps go with a pickled pepper like pappadew.

I LOVE dill...its one of my favorite herbs, and it goes well with cheddar. Other than that, I would stay light and summery with chives or tarragon. Thyme would work, but it wouldn't be my first choice. If you had a use for fennel bulb, I love using the frond as an herb...but I wouldn't suggest anyone waste a bulb for the herb, however when I use fennel, I nearly always use the frond as a garnish. Chervil has a similar-isn flavor and isn't used often. A lovely French cornerstone called "fines herbes" would be lovely if you can find it. Its generally a mixture of fresh chervil, tarragon, parsley and chives.

I hope some of that helps haha.

Personally, I'd go more with a dried chili powder than an herb like oregano or dill. A little cumin would be nice. I think I'm in a Southwest mood lately. Dill does go nicely with cheddar, so that may be a good choice too.