I've only ever had one 99, that being cooking. I spent two weeks working on it during school holidays once. It's pretty quick, and you considering you can browse Sythe, Watch TV/Youtube at the same time, it's a pretty easy one too.
Unfortunately my beast f2p pure (99 magic, 99 range, 99 strength, 40 attack, 1 prayer) was banned for botting about 8 months ago so unfortunately atm I have no account with a 99 stat. My new f2p pure doesn't even come close (max stat is 84 range).