There is no resolution limit for 360cities.
Normal uploads depend on the TIFF limit (4GB, about 90,000 pixels width), but larger images can be published. The ability to switch the rendering method is another attractive feature.
The Basic plan (free) requires a review initially, so it will take some time before you can publish after uploading, but once you are certified as an expert, no review is required.
It's hard to say that the quality of the images is great, but it's a trade-off for the lightness of browsing, so you may have to live with it.