No, don't get a manual focus lens. You will lose your patience.
(and let's face it, much more sense-making)
1) It depends on what kind of lens we're talking about
Clearly, the ergonomics of a manual focus wide-angle lens are far, far different than a long tele. Focusing with an MF 28mm lens is piece of cake. Focusing with a 300mm one is an entirely different story. For ultra-wides in particular, you could pretty much pre-focus your lens and be all set! I'm not kidding. A 10mm (DX; 15mm for FX) lens at f/11 can be pre-focused on 45cm and give you (if you do the calculations with a DOF calculator) near-focus limit of 22.5cm until infinity! So, unless you wanna go closer than 22.5cm or have a larger aperture, you don't even need to worry about focus.
But check out the numbers on a 300mm lens at the same aperture:
For an object at a distance of 10m, the near-limit is 9.76m. The far limit is 10.2m. That's a DOF less than 0.5m deep. Now, that can be a tricky thing...
|Still shot, very controlled. And yet, the focus is off. I was going for the eyes, but the focus is on the blouse. Especially with long teles, manual focus is difficult|
a 60mm macro that will be mostly used at f/8-f/11 is an entirely different animal than a 50mm f/1.4 lens that will be used wide-open.
2) It depends on what kind of photos we're talking about
You can guess that yourself: Will you be taking photos of running children? Forget manual focus. Will you be getting macros of still-life, carefully arranged in your home studio? Prefer manual focus.
3) It depends on what kind of camera you have
This might create some controversy, but it shouldn't. Let's face it, some cameras are simply better than others for manual focus. Big and bright viewfinders are obviously better. Simple focus confirmation dots are not as great as systems employing dots and left/right arrows, to show you focus direction. Plus, entry level cameras won't even meter with manual focus lenses. To put it this way, on my D700 (which offers all of the above), I would use a manual focus lens that I would simply not bother with on a D3200.
4) It depends on what kind of photographer you are
Are you patient? Are you willing to work around issues? Are you the kind of guy who could imagine trying a sports event with a manual focus lens? You don't even need an answer to those questions, you see where I'm getting with them.
|Sports with a manual focus lens? It can happen - impossible is nothing. But it's a real pain, I don't recommend it! This one was with a Nikkor 50mm f/2|
5) It depends on how much you want to spend
Generally speaking, the autofocus variety of a given lens will be at least 30% more expensive (and if it's the AF-S variety, probably more). Optically they should be identical - sometimes the manual focus might even be better! Is it really worth to pay so much more for the convenience? Again, it depends. micro-Nikkor 105mm f/2.8 AI-S, about $300. AF-S VR 105mm f/2.8, about $700. Definitely not worth it. But:
Nikkor AI-S 50mm f/1.4, about $150. Nikkor AF-D 50mm f/1.4, about $200. Definitely worth it!
In the end, I would say if there is an autofocus lens that is optically as or almost as good as a manual focus one, get it (with macro and wide-angle being the only exceptions, really). Ultimately, even if a manual focus lens is cheaper (and even better), there is little point in preferring it if you need to take 10 shots to get a sharp one.