Best versatile camera lens?

I currently shoot with a Nikon 18-200 and instead of buying a new camera (currently have an old d3100 but she gets the job done) I was looking to get a new lens and I think I've done too much research cause I'm lost. I mainly shoot landscape and nature photography so I'd love a lens that suits that but I also is good for portrait photography and maybe street/architecture photography, I know it's a lot to ask of a lens but what recommendations do you have?

Your current lenses will pretty much do what you want it to be. The only downside of an 18 mm to 200 mm is that they are typically relatively slow lenses.

Sounds like you're itchy for a new toy.

There's nothing wrong with the 18-200. It covers landscape to portrait and the occasional need for telephoto. What can't this lens do for you? Answer that and you'll get better suggestions. I use the 18-140 for 80 to 90% of my shooting which is generally nature related (landscape and critters). I have other specialized lenses for other tasks which don't get used much.

What the 18-200 lacks is a big aperture (small f-number) which is handy for low-light and selective focus. Portrait shots can benefit from a larger aperture for selective focus (blurring the background).

If you want to do portraits on a crop sensor camera, get the 50mm f/1.8 lens. It's reasonably priced and you will have the benefit of selective focus. If you like shooting flowers, the 60mm f/2.8 macro will do nicely for close-up shots of flowers and will work nicely as a portrait lens.

If you want to do architecture, an ultra wide lens can be the ticket. You can find zoom lenses in the 10 to 20mm range. Using an UW lens requires learning how to shoot with one to prevent converging lines. This is a wonderful lens for aurora shots. They are also fun lenses to take closeups of faces due to perspective distortion, but I digress.

You don't state a specific budget, but considering the gear you already own, I'll assume it's in the sub $1,000 price range.

All-in-one lenses such as your Nikon 18-200mm are going to be okay for all of the various different types of photography that you mentioned, but it won't be great for any of them. That's the trade off that you make by trying to get just one lens that does everything. You can, but while it will do everything okay, it won't do anything better than that.

An 18mm lens is okay for landscapes, but what you'd really like to have is an ultra-wide lens (prime or zoom). Most people prefer the zooms over primes because they're far more versatile and take up less space and cost less than 3-5 prime lenses. Look for a 10-22mm or some other range that starts off at 10mm. That will be the best type of zoom lens for landscapes.

The term "nature" is vague as it refers to macro shots of bugs and flowers, landscapes, wildlife, and just about anything else you can think of that you'd commonly find out in nature. Each of these types of photography will be best done with different lenses. Macro for bugs and flowers, telephoto for wildlife, and ultra-wide lenses for landscapes.

Macro - A macro lens has a reproduction ratio of 1:1 which means that the image you're taking is being projected onto the sensor at life size. A lens like you 18-200 has a "macro" setting which produces an image about 1:4 or 1/4 life size. Lenses in the 60-100mm range are going to allow you to shoot further away as the focal length increases, but this is not to say that a 100mm macro gets a tighter or closer shot than a 50mm. Both lenses produce a 1:1 reproduction, but the 100mm macro will do it at 2x the distance. So while you're 2x further away, the magnification of a 100mm is 2x stronger than a 50mm, so the additional distance is canceled out by the longer focal length. The benefit of a 100mm macro is that can be used for macro but also portraits, so you kind of get two great lenses for the price of one. This, and the fact that you're further away so you don't scare off bugs, is why macro lenses in the 90~105mm range are so popular.

You could just get an extension tube for the Nikon F mount and get macro that way which will cost you less than $90 as opposed to a $450 1:1 macro lens.

Based upon what you state is your intended subject matter, it doesn't seem like you need another lens unless your current lens is not wide enough for landscapes or strong enough for wildlife. A better solution is to get lenses that are specific for the types of shots that you do as opposed to an all-in-one solution. The focusing will typically be faster, the aperture will be larger especially in the telephoto position, and the lens will be optically superior, too.

So to really help you out, you have to state what is it about your current 18-200mm that isn't' working for you because if all you had was the 18-55mm kit lens, I'd be recommending the 18-200mm as an all-in-one solution for the types of shots that you've listed.

An ultrawide zoom will do what you want. There are several that will autofocus with your D3100, from Nikon, Tamron, and Sigma. Something in the 10-12mm to start range, like the Nikon 10-22. For architecture, you will have to learn how to use a lens this wide so that your lines are curved all over the place, but that's half the fun.

An ultrawide and your 18-200 will cover just about anything except maybe chasing birds in flight or other wildlife (or airshow) work.

I just use my 18-55 that came with my D7500 for wide shots, as I don't use that end of the scale much. On the rare occasion I want wider… I can take 2 or 3 shots and merge them later.

My walk around lens is either the Nikon 70-300 AF-P or a Sigma 150-600 C.

One lens? You have it already. Want more? Tamron 18-400mm! Now that's the most you can get in the versatility department. If you want a bit more on the wide end for your landscapes, see the Tamron 16-300mm.

Now if you want best, break up the zoom into shorter ranges. Get a wide angle lens for landscape and some nature. Get a standard lens for some people and some nature. Get a short telephoto lens for portraits and some nature. Then get a really long lens for wildlife if you're into that kind of nature. Heck, throw in a 100mm macro too for those tiny critters and flowers along the way. You can get zooms or primes. It's up to you.

18 to 200 covers most eventualities. Tamron does make a 16 to 300, but the wide-angle end is the hardest to design, for good technical reasons, so I would be wary of trying for those 2 extra millimetres, which would not make a huge difference over 18mm.

What limitations do you find with the 18 to 200? 18 gives good medium wide-angle, 200 give fairly good telephoto reach. For shy wildlife you might want a longer lens, so maybe get a 120 to 500 or to 600 solely for the wildlife. If 18mm is really not wide enough, get a lens of around 10mm to 17mm for seriously wide applications.

I had forgotten about the Tamron 18 to 400, thanks to Keerok for the reminder. That might be the lens for you.

The idea of DSLR is that it has interchangeable lenses.
If you want a single lens tp do everything then get a bridge camera.

Something like a 24mm to 100mm or the Nikon dx equivalent. I find those superzooms annoying and cumbersome. Failing that a fast 50mm.