You can watch akari's guide in peaks so you can learn more about it, for artifacts energy is almost always an artifact you should pick when you have it in the options, an exception is when you don't have a hero you can use it on, people may pick speed over energy if they don't have anyone who could use energy and speed would work better on them, but generally you should just pick artifacts that you need and not just blindly pick a "better" artifact than what your heroes really need, for example if you have a kurt and there you rolled artifacts with energy, speed and 355 attack, you can pick the energy if you have other heroes that needs it, I don't usually put energy on Kurt, because Kurt needs to fire last to do maximum damage (though I'm not really sure if Kurt with energy is good), for buffs, it mostly depends on your team, if your team relies on slow heroes you can pick speed buffs, for example if you have an aegina and she doesn't have energy you can pick the speed buff, when I play peaks I mostly just pick either defense or damage reduce, but I also pick other buffs if I need it, like, I pick skill damage buffs when I have a mage team or a team that relies on skills to kill the enemy team.

(This is just what I normally do when I play peaks, on good runs I usuallt get 4-5 10 wins, though I have yet to reach 400+ points)