I've been on both.
First iPhone was a 3G, yeah, that one was a turd. Didn't buy it at launch though, bought it later on in the year.
Held that turd, smashed screen and all for about 2.5 years, until the 4S. Got that on launch day. That phone was phenomenal, and compared the the 3G the design was amazing, even though it was already an old design.
When I was due for an upgrade (back in the days of 18-20 month upgrades), I figured I was foolish not to take the upgrade whenever it was ready, basically meaning I'd get two out of every three phones. So I got a 5 in May of 2013. Great phone but had the defective battery. It was nice, but didn't seem like that big of a deal since it really wasn't a lot different than the 4/4S.
Ditched that contract early to switch carriers and got a launch day 6. Absolutely love it. Now that upgrades are 24 months, and with no plans to switch carriers, I'm on the initial cycle for good and should be able to get right on or right around launch day, depending how anal Verizon is with launch day upgrades depending what day of the month preorders begin.
Given my history it might sound like I'd prefer the S cycle, but I really don't. While it's nice to have a case and screen protector ready to go on day 1 with the S cycle, it's worth putting up with the initial accessory delays to have the newest thing IMO (lots of manufacturers still struggling with the iP6 accessories). Maybe it's just that the 5/5S weren't terribly different in design than the 4/4S, but by the time the 6 came out I was way more than ready for a design change.
Pros and cons to each, but Apple is slow to redesign things, so it's nice to get it while it's fresh.