Hi, I'm new here, and I was just wondering what Sylesti you thought was the best?

whatever sylesti a person likes- really it depends on what is being classified by the term 'best'

By appearance, it's entirely subjective

By species, they're all technically equal, since all species can be bred to achieve the same max stat point eventually. (though with first generation sylesti there are ones that are better than others)

For battle, generally people go for max stats (2000 hp, 200 mana, 100 str/int/dex/agi, eg this), superstats (pet that is over max with + stats, eg this) supermaxes (pets that have both max stats AND + stats, eg this) (though they do still generally pick by appearance preference what ones they use)
They aren't necessary, though they do make it- often a lot- easier, but they generally have price tags to match the effort to make them.

(I personally have my own main team who are not max (stats averaging around base 79) and hold the high distinction of having beaten the toughest challenges the game has to offer, so it is POSSIBLE but it is definitely hard. I keep using my main team because I'm attached to them. for ME they are Best Sylesti.)

Oh!

Thank you so so much!

-Lulu