I started with the 3G, skipped the 3GS, and got the 4 after dabbling in WP7 (love the OS, hated the Samsung Focus). I then found a great deal on a 4S off contract and bought it and sold my 4, and have been rocking with it since. It's amazing how much faster the single-to-dual core change was. My mom's iPhone 4 feels like a dinosaur to the 4S (can only imagine the 5). I'm off contract with AT&T and am awaiting the 5S. I feel like the S cycle has many benefits to customers, as Apple works through manufacturing issues with a new design and internals for a year, and the customer gets a more refined product. One of the biggest manufacturing issues for the 5 for me is the soft aluminum and anodization that wears away. I do not like that, and hope that's fixed for the 5S.
For me, while I'd absolutely love a bigger screen (same height and more width would be dope), a revamped iOS 7 and subsequent jailbreak, larger sensor and enhanced camera features, NFC, base model at 32GB, 2GB RAM, and better battery life would be great and would most likely keep me away from the One, Xperia Z, and S4.