If you don't mind losing out on the security updates and the continuity features with OS X Yosemite, then it's fine to stay with 7.1.2. App compatibility though will become more of an issue as developers start using the new APIs built into iOS 8. Compared to iOS 7, which focused on UI changes and transitioning to 64-bit, iOS 8 has much more extensive developer-focused changes.
I've been on iOS 8 since day one, and right now, my 5s is at least as stable and fast with 8.1.2 as it was with 7.1.2. I generally recommend updating using iTunes (which replaces the entire OS directory at once, rather than updating the files piecemeal), since it seems that recent issues have impacted devices updated OTA more frequently. Keep in mind when comparing "speeds", that there are a lot of variables in play (i.e., when the device was last rebooted, whether the caches were recently purged, how many apps are running in the background, whether background refresh is active, whether location services are running, the signal strength, etc.).
Also keep in mind that the 5s running the early iOS 7 was not particularly stable, and had its fair share of performance issues. Comparing to the early versions of iOS 7, iOS 8 has been far more stable with fewer issues on my 5s.