We went through the market evaluation exercise last December for a client that wanted to replace the couple they had - two reasonably cheap ones were used for prototyping and then they had three dearer ones for production work. Their budget was <$5k per unit.
I leant a lot more about them than I knew in working with their team so the best advice I can give you is to decide what you want to use it for, particularly in terms of materials it can work with, as that will determine a short list for you.
So, for example, every machine on the market can work with PLA (Polylactic Acid) and it's the most widely used filament but not all of them will work with the high-tensile version PLA-T. In itself, PLA is an amazing polymer and there are variants that mimic wood, silk, have glitter or colour changing effects and even carbon fibre impregnated PLA although not all machines can handle all variants. It's also food-safe and reasonably environmentally friendly.
ABS (Acrylonitrile Butadiene Styrene) filament is the next most widely used for home printing, favoured for its strength and ease of use but it's definitely not friendly to the environment and not every machine can work with it.
PET-G (Polyethylene Terephthalate enhanced with glycol) is the next most widely used as it is extremely strong and easy to work with having the best qualities of PLA and
ABS in one material. Again, not all printers can produce the heat (235
oC) required for it but I'd consider it a good capability to have.
Amongst the rarer (and less supported) but useful materials are:
TPE (Thermoplastic Elastomer) which while not supported by many machines is a soft rubber-like material capable of being squashed and stretched after printing.
Carbon Fiber filaments mixed with other filaments beside PLA or in higher concentrations.
Metal filaments which include Copper, Bronze, Brass and Stainless Steel are only supported by a couple of expensive machines but the benefits are obvious.
It's probably not relevant for you but they ended up choosing the Flashforge Creator for the prototyping because it handles a wide range of materials including nylon filaments; comes with two heads and has the highest plate temperature on the market (note that's the plate not the printing temp). On the downside, it's not as fast as some machines and doesn't support other nozzle sizes.
They stuck with Flashforge for the production machines, choosing the Guider IIs for all of the reasons above plus it's a lot faster albeit about 2.5x the price!