Inquiry is probably easier, but if you are in science and a hard worker, you shouldn't take inquiry.
I've been in that course for 3 weeks before taking astronomy, and it was the WORST! The prof hasn't showed up one week, and the course work is very obscure! On the first day some strange prof showed up, took us outside to a tree and gave us an article. Then there were some subjective "debate questions" afterwards.
I didn't really like it because there was no real science, and there was some very strange course. However, it is very easy as you show up for 2 hours each week, course work is minimal, and at the end you ask for the mark you want and the prof decides whether to give it to you :S. (Keep in mind that was 2 years ago and it was 1SC6, so it may have changed a bit)
I would suggest you keep 1SC3 as your second term course because it is limited, and you can switch to psych 1AA3 second term if you like the 1A03 course. Psych is usually easier to switch into than inquiry.
Comparing env sci and inquiry: they are both very easy courses. It's up to you whether you want to learn something or not. If you don't, take inquiry.
Nonetheless, I would suggest keep inquiry and switch into something else second term if you like, but DON'T MISS THE DEADLINE IN DECEMBER OR JANUARY!
Paul