These FFT analysers are all suitable for vibration and acoustic diagnosis work. They are expensive and complex instruments. I've included comments about the ones I've used, if you are a newbie I'd go for the one that has the best training, or that your main customer uses.
Bruel and Kjaer
I've been using their gear for twenty years. The front ends, amplifiers and transducers are generally excellent. I'm not the world's biggest fan of B&K analysers, the menu structure can be confusing and some of their design decisions are odd.
B&K 2144 I've used this one, and like it. The driveby noise analysis add-on is excellent. The sound intensity add-on is one of the better ones around.
Agilent (ex HP) I prefer HP twin channel FFT analysers to any other. They generally have a consistent interface, and are pretty reliable. The best general purpose analyser I have ever used is the 3562A, no longer made, and any you find may be getting unreliable.
I've only played with this one's predecessor, I think, and have used an older 4 channel for a long time. Lovely screen for a portable. Ono Sokki's menus and manuals tend to be a bit idiosyncratic, rather like the B&K they often put specific features in that are incredibly powerful, but take a bit of head scratching to figure out.
The following three are laptop based systems, all of which seem to be rather good. Note that the laptop systems are rather expensive, and not very durable, compared with the one box systems above (although watch the cost of the one-box systems as you add options). On the other hand they have a lot of channels available and data storage direct to hard drive or CD is pretty wonderful. I'd be inclined to use a cheap laptop with a CDRW back at the office and just throw the laptop away when the case gets too beaten up, or the screen falls off etc etc.
B&K Portable Pulse Specs look good, we may switch over to this. I haven't used it. The Pulse front end is versatile and powerful, if a little obscure at first sight. Keep hitting buttons (there aren't many) and it all becomes clear.
Prosig supply front ends and software for laptops. The software is powerful and easy to customise, although the learning curve may be a bit steeper than some of the other products here. One of their great advantages is that they are very very helpful. The data acquisition task is good, it takes a while to set up and then it makes standard tests easy to take.
You'll have to search the site for the Pimento yourself. Good, powerful software suite. I haven't used it, I have used the older LMS software for many years. Sticker-shock warning. Support is pretty good, at least in Australia.