Things to consider:
DPI, the higher the resolution, the finer the print.
Paper Path: the straighter the better.
Single Path printing: where the paper only goes through once, rather than 4 times, as registration of the colours more accurate.
Most modern laser printers use separate colo(u)r carts, this is preferable.
Availability & cost of carts: No point in getting a sub-USD$200 printer if the set of carts cost $800+ ?
Also TCO; total cost of ownership (all costs divided by printed sheets produced = cost per sheet)
Buy carts in sets & online much cheaper.
Interoperability: If you have one already, try to get an improved model of printer that takes the same carts, saves on dead $ tied up in carts & you could always 'borrow' the other one?