have been pondering over this for the last few weeks as well. Still havent been able to decide on calf vs suede but out of your options, i would lean towards the first one, i think the lighter colour would be better for summer. The darker suede seems a little heavy?
As for the calf one looking too formal, its a question i have myself.
This is my conundrum too. I like the lighter calf better but feel a suede would be a little more casual. The main thing I want to avoid is my shoes being too dark and like you say, look heavy.