I've seen all the seasons (: the first season that I saw, though was SHINee, and it's my favorite :D I loved the whole concept of 'babies looking after a baby' lol it was so much fun! SHINee is so playful and they were so enthusiastic, I think all SM artists do really well in variety shows haha
but i can't NOT mention MBLAQ's Hello Baby, that one was so freakin' hillarious too, and I loved how from the very start, everything was challenging, even finding their own babies :D i'd heard their music, but I didn't know any of the members before that show, and I ended up loving them all! especially Seungho the kind daddy and Mir, the playful goof :D I also really loved how Lee Joon tried so hard to get the babies to like him, he was so determined!
I REEEEAAALLLY hope they make another season with another group - Big Bang Hello Baby? or B.A.P Hello Baby? it would be so fun watching Zelo interact with another baby XD