The first feature I thought of was "Define". Select a word anywhere and tap define. It's a simple feature, works system wide without taking me away from what I'm doing and enhances my vocabulary.
Secondly, Reader. Safari's built in "get the crap out of the way and let me absorb the information I came here for" feature is indispensable, invaluable, priceless, unique and vital.
Next up, variable speed media scrubbing. Need I say more?
Legible font. I don't know about other people but for me the font on iOS devices is legible at arms length at just about any size. Less pinching and zooming attempting to be able to read text lets me be more efficient get what I came for and be on with my day.
Location based reminders. Ok maybe I don't use these everyday, but often enough to warrant mentioning them. I don't always know when I'm leaving or arriving.
Speak selection. I use this feature daily, multiple times throughout the day. TTS in all its glory. Whether its just to read an article to me while I do other things or to help pronounce some of those more complicated scientific terms the Speak Text feature is a must have for me.
Move selection. Hold down your finger, something gets selected, move your finger to select something else. Very useful and time saving. I find it much quicker than zooming in and selecting a word or text on fine print or small text.
Scrolling text selection. This feature mainly works in Reader or Define. Hold one finger on the appropriate slider and scroll with another finger. It's faster than the automatic scrolling of just dragging the market up or down and selects paragraphs at a time. If you're similar to me and Reader is a staple of your iOS diet then this helps you take care of business and get on with your day.
Select all. Highlight something near the top and drag the left slider upwards past everything until you see the screen go blue. This works on most web pages, in Reader, in define and with quite a few other things. The options given them are usually Copy/Speak.
While there are a multitude of features I could go on about which I use daily, the list is getting long as it is. Please feel free to post and let me know if other platforms have these features or what features you use daily which you just couldn't live without. Stay classy iMore.