Finding the right gear can be an expensive trail and error experience or at least one that will have you banned from returning items to any number of stores. Glass, for me, is some of the most difficult pieces of gear to buy as lenses can have the greatest influence over picture quality and, bourgeois, sharpness. This importance is doubly so for those on a budget as getting the best value for your money becomes a prominent concern. There are plenty of user reviews available and sites like DXOMark attempt to provide an objective rating system (more on that later) but ultimately using a lens is the best means to see if it's right for you. With that said, below and in a forthcoming Part 2 I've outlined what glass I've used on my D750 and my thoughts on each.
AF-S NIKKOR 14-24mm F2.8G ED
The first of the 'Holy Trinity' or whatever goofy name for the three Nikon lenses that cover a range of 14-200mm someone decides to use. Names aside, this lens is highly regarded and for good reason. There's minor distortion, even less vignetting, flaring is rarely an issue, and it is incredibly sharp. Although great for landscapes, I primarily use this lens for real estate photos. This lens isn't for everyone, as ultra-wide angle tends to be a bit more exclusive in use, especially at a price of $1899 but if you did need an ultra wide-angle lens then you couldn't do better than this one.
AF-S NIKKOR 20mm f/1.8G ED
I only had this lens for one job before I switched to the 14-24 but I was happy with the results. Sharp, minimal distortion and flaring, and has a distinctive sunstars which some may or may not like. Not too pricey, current price at $799.95, and has the advantage over the 14-24 in having a standard filter size. This is also the widest non-fisheye lens Nikon makes that is less than $1000 so it's an excellent choice if you need a wide angle lens and the 14-24 is too pricey.
AF-S NIKKOR 24-70mm F2.8G ED
The second in the 'Holy Trinity' of Nikon lenses. I used to think of myself as a prime shooter before this lens but now this is on my camera more often than not. The focal range is great for the type of work I do so rarely do I feel a need to switch to a prime lens or another lens. The current price is $1669 but because these are so popular, and since the release of the VR version, you can sometimes find one used in excellent condition for around $1000. That's a great price for this lens and I hesitate to suggest buying one new because used ones are much more affordable. The only real downside to this lens is that it's not as sharp as the f/1.8 primes within similar focal lengths especially at either end. This is to be expected for a zoom versus a prime of course but to me the quality of every other aspect of this lens outweighs a minor loss in sharpness.
AF-S NIKKOR 24-120mm f/4G ED VR
When I bought my D750, the store I was purchasing from only had it packed with this lens. Someone else was trying to purchase the camera without the lens and because I offered to buy both I managed to get it out from under him. I wasn't sure what to expect from this lens as I think of it as a kit lens which usually doesn't imply quality. As the case most often is, I was wrong and was surprised by this lens. Although soft on the extremes of it's focal range the lens is quite sharp in between. There is some distortion and vignetting but no more than one might expect for a zoom lens with such a large focal range. The constant f/4 aperture although a bit slow is offset by VR and is fairly sharp wide open. The nano crystal coating reduces flare as intended and is a nice bonus. The only real problem is the price and who this lens is intended for. With the D750 it'll cost about $600 extra and buying separately you can usually get an excellent quality used copy for roughly the same price, a new copy costs around $1100. If you're on a strict budget this might be the single lens to get but I wouldn't suggest buying full frame on a strict budget anyways. It might be a great everyday use, "do all" lens or one to travel with, as it is compact for its focal range, but those type of uses may be better served by other glass or camera systems. It's not that this is a bad lens at all but I'm just not sure who it's for.
AF-S NIKKOR 35mm f/1.8G ED
This is the only Nikon lens I've used that I've been disappointed in. I've used the majority of the f/1.8 primes from Nikon and have always been impressed with their sharpness and quality but this one feels like the weakest of the bunch. For a 35mm it has quite a bit of distortion and vignetting and is noticeably soft wide open. Stopping down fixes these, as does post processing for the former two, but that's not what I've come to expect from Nikon's f/1.8 primes. Because of this it doesn't seem to be a great value at $529. I generally prefer to buy first party when it comes to glass and other accessories but if you're looking for a 35mm I would suggest taking a look at Tamron or Sigma.
Sigma 35mm F1.4 DG HSM
I rented this lens to use for a few shoots as Sigma's Art line gets a lot of praise and reviews for glass in this line are generally favorable. The lens is large, heavy, and doesn't have weather sealing but those are the only drawbacks of this lens. It's tack sharp, has good color rendition, offers minimal distortion and vignetting, and has a great feel and build quality. At $899 this lens is closer to the $529 Nikon 35mm f/1.8 price wise than the Nikon 35mm f/1.4 at $1699 and as I stated above I wasn't impressed with the NIkon f/1.8 so the Sigma is definitely worth the extra cost. Versus the Nikon f/1.4 the value for the Sigma is tremendous as this lens is so impressive. In full disclosure, I haven't used the Nikon f/1.4 but I can't imagine there being any advantages to it for the additional $800 in cost