I've been using Archidekt. I really like the built-in playtester, but the interface can be kind of sluggish, and some of the design decisions, especially around categorizing and sorting, are quite clunky.
I know there are a lot of options but I haven't tried any of them. Are there any that you'd recommend?
I've used tappedout.net since as far as I can remember. I don't think it's better than the alternatives, I use it mostly just out of habit.
I like scryfall.com's deckbuilder too.