When looking at the specification table for each knife, you may want to look for:
Bevel angle ratio:
A western style knife with 50/50 bevel angle ratio can be used by right or left-handed people. You only need to worry about whether the knife is left handed or not if you're looking for an asymmetrical knife.
HRC:
The Hardness Rockwell C scale represents the hardness of the metal. Knives with a higher HRC, in general, retain their edge for longer but are, generally, more brittle so beginners should look for a Western style knife with an HRC of 58-60 if they need a more durable blade or Japanese style knife with an HRC of up to 68 (in more extreme cases). Not all steels behave the same at higher hardness and higher hardness is not the sole determining factor of knife performance.
Blade material:
If you are just making a foray into Japanese knives and are worried about the level of care you might need to put forth, consider getting a knife made of the simpler Molybdenum Vanadium steels or knives marked INOX (meaning stainless). These knife steels are usually heat treated closer to 57-59 and are a little tougher, more ductile and hence more resistant to chipping; they are easy to sharpen but the edge retention and peak sharpness will not be as high as the more advanced stainless steels or carbon steels.
If you’re a more advanced user of knives and you’re comfortable putting more care and effort into them, consider using some of the higher hardness, more complex stainless steels like VG10, R2/SG2, SRS-15, AEB-L, HAP40 or ZDP-189 among others. These steels will offer a variety of benefits over their simpler stainless counterparts depending on the steel but generally have higher edge retention, a little bit harder to sharpen (more time spent) but can often take a better edge than the simpler stainless steels.
Finally, there are the carbon steels. These are suitable for users of all skill levels; however, they are prone to rust so those who want to use these steels need to be aware of a slightly higher maintenance requirement. Carbon steels will almost all be easier to sharpen and take a keener edge than comparable stainless steels. They will not necessarily have better edge retention though. Beginners should consider Hitachi yellow, SK or white 3 steels while more advanced users should look to white 1 and 2 for simple steels that will take a very sharp edge or blue 1, 2 or super for those looking for great edge-taking as well as better edge retention. The blue steels will be more difficult to sharpen due to their higher hardness and carbide content, so we recommend these steels to professionals.
Size:
Of course, a larger knife means that you can do more work with it. However, if your workspace does not accommodate a larger knife then its increased real estate is largely wasted. You should make sure that the knife you’re looking to purchase is not longer than your cutting board is wide. On the other hand, you do not want a knife that will be too small to perform tasks that you do every day. For instance, if you plan to chiffonade a head of iceberg lettuce, you would want a knife that is at a minimum longer than the average head of lettuce.