Szimpla Kert is *the* ruin bar to visit as a tourist. It's the original and the decor is so very eclectic and interesting. I obviously only saw one other ruin bar to compare with but people who know best online have agreed it such. It's the place to be when you want to hear English and as a result the difficulty and competition to get in during the evening with the drunk young crowd is really only if you want to be one too. And likely sweat amongst them also. I don't doubt the atmosphere is fun though.
A recommended way for the less imposing is to visit easily during the day when everything is quiet and subdued. There is a very nice looking farmer's weekend brunch buffet that I would have liked to try and otherwise coffees and housemade lemonades to choose from.
I think I preferred it this way and finding another quieter ruin to peacefully drink and chat in the evening (which ended up being Csendes http://eatlikeushi.posthaven.com/csendes-budapest-11-2017).