Summer - Swedish summers can actually be just as warm and pretty as the summers in the south, perhaps not quite as often, but it's fairly normal with temperatures above 25° C.
One of the best things about Swedish summers is the fact that they are very bright, it literally never gets truly dark and I find this really pleasant, especially since the winters are the complete opposite - cold and extremely dark.
And for that reason my least favourite season incidentally happens to be the winter.

I was on vacation in Greece last summer and when we got back home it was almost exactly as warm there in the morning as it had been when we left Greece - somewhere in the 25° C region.
And daylight at six o'clock, and lush greenery everywhere.
Beautiful.