I tend to leave mine on auto focus most of the time, ok yes it can be abit slow but im not exactly the fastest at manually finding the right focus, also when i se the manual i can't tell if im focused or not!!
I think it all depends on what you are taking a picture of, this is defo the case for me.
I've been a bit spoiled to Auto, but if I'm doing still life, I go manual - when you're at a horse show photographing 20+ horses in a class and they're circling around you all at different spots in the arena and various lengths away from you, I use Auto. Same for if they're out running crazy. Ferrets? PFFFFT good luck with manual. Portraits are manual, if the subject is being relatively still, manual. It all just depends on what's working at the moment and what's not.
Slow is no problem for landscapes, nature, and still life, but it can be a pain with events and moving subjects. Maual focus may be too slow then also.
There is the photojournalist approach of 'f8 and be there'. That is preset the camera at f8 or something that gives you lots of depth of field so you can manually focus and shoot quickly and it won't matter if you are slightly off. Manual focus can be tricky for digital cameras as the focusing screen is not really designed for it. It is easier with cameras with large viewfinders (like full frames) or those that have a focusing aid like focus peaking.
I think autofocus is very useful for a beginner. You can use little tricks like holding the shutter button down halfway while focusing on something else then moving the camera back to take the shot. It helps you to concentrate on getting the basics first. I tried using manual focus when I first started, but the photos turned out blurry because I could not see how it was in the viewfinder well enough, which was very discouraging. Once you've gotten things down like composition, lighting etc. You can try manual focus. Now whenever I take portraits I use manual focus because it gives you more power to have the photo the way you want it, but it takes some getting used to. I still have blurry photos from time to time.
Perhaps this isn't the best advice, but it worked out well enough for me