I did both zip lines and I will whole-heartedly say to go ahead and do the higher, superman-style zip line. It goes faster, it's longer, higher and overall, just more fun. My friend and I went early afternoon on a weekday in June and there was no wait at all. I would've preferred to go at night but it just didn't fit with our schedule. But again, NO LINES, so it worked out well.
The automated machines to buy your tickets were awesome. Just walk up, pick a time, pay with a credit card, get your wristbands, then walk up to the stair case once your reservation time is shown. Super easy!
The only reason for 4 stars is that it's pricey (but did you expect otherwise?) for what it is. And they'll get you on buying photos, too. But it's a once in a lifetime thing, so do it, live it and get the photos :)
Side note: I love Fremont but don't think just because you come in the daytime that it's PG. Leave your kiddies at home if naked randoms bother you!