Bing image creator let's you use DallE 3 (which is considered one of the best) for free for now. After you use up your lifetime of tokens your pictures are processed slower.
leonardo.ai is nice because your tokens replenish daily and it's easier for you to tweak your results.
Both let you upgrade to premium if you want. I'm not a fan of services that have no free tier because there's no way to know if the results are good until you start using them.