I'm always looking for information on what my class companions skill bonus, what's their main stats or what gifts they like to get affections up. So I collected a bit of information on each companion and took note on a file on their most important information. At least saves me the work to go all over the internet or the codex to see what they can wear. Or also helps me to plan out what crew skills I should pick, considering the companions of my class.
Besides the information about the companions, I think it's also important to know what each crew skill does and what they require, i.e. what gathering skills should one pick. So I also compiled a small information about it:
After considering the dependencies over each crew skill and knowing which bonus each of my companion gives to a certain crew skill, I can decide which I should pick. Like for example, the Trooper for the Republic, have companions that give bonus to Biochem, and also the gathering counterpart of it Diplomacy and Bioanalysis. So picking Biochem for it, would be interesting. The same thing happens for Agent on the empire side
This is not mandatory, but can help players pick what they really want, and take advantage of it.
So for the Republic side:
And the Empire:
There's also information about what weapons they use, what's their main stat (endurance is always second stat for any companion) and what gift types they prefer. Hope this helps somewhat.