nikon 28-300 or 70-300? I don't really understand all the details about lenses. Right now I have the 70-200 f2.8 and it is too large and heavy for me to bring with me and carry conveniently when I travel. I'm looking for a nice lens to replace it that will give me good zoom to photograph wildlife. Can someone please suggest which lense would be best for this purpose? The nikon 28-300mm f/3.5-5.6G or the 70-300mm f/4.5-5.6G? The 28-300 says it has 10.7x zoom versus the other has only 4.3x. So I would get closer images with the 28-300, but are they still going to be good quality?
NO, the difference between the two lenses is at the wide end, which is mostly needed when you shoot landscapes. The 28-300 gives you coverage of the 28-70mm range which the other one does not. At the long end, shooting distant objects (which is what you do most of the time when you shoot wildlife) the two lens are identical in coverage and image quality.
If your primary subject is animals and birds then the 70-300 will do very nicely for you. Except in very poor light the image quality will equal what your 70-200/2.8 bazooka is doing. If you also like to shoot landscapes (or on the rare occasion when an elephant comes really close to the car) you will miss the wide-angle coverage. You will also miss the wide-angle coverage when you are at home taking pictures of friends and family.
If you have a Nikon you probably have an 18-55 kit lens already, which will complement your 70-300 and give you a full range. Enjoying that full range, however, requires you to change lenses in the field. "The field" if you happen to be on safari, can be very very dusty, so a single all-purpose lens is the better idea. The 28-300 will set you back an extra $400 or so, but many photographers have already figured out that the exra cost is money well spent, which is why the 28-300 has become quite rare.
One final note, both the lenses you are considering are quite big and heavy, though not as big as the bazooka you have now. If carrying a big lens is an issue for you it is advisable to go to a camera store and actually handle the lens before you commit to it.
the reason why you have a 2.8 is to enjoy shooting wide open when all other lenses require you to stop down even more. You pay for in price and weight. If you have a FX sensor and willing to drop down to the 3.5-5.6 (plus more to get crisp shots) this is the only lens that works. Most people don't travel with 2.8's if you want a cheaper options don't go to zooms and stick with primes.. this allows you the 1.4-2.8 to show in low light BUT you have to change lenses and you can miss 'once in the lifetime shots'.