Timid. When you are choosing a nature, you want one that increases the stat that benefits the mon the most while reducing the one most unnecessary. In Togekiss' case, this would either be timid or modest because its atk stat is only fifty compared to its a hundred and twenty spa, a significant diffirence. On the special side, Togekiss also gets a lot of good coverege moves like flamethrower and aura sphere. Most importantly, if you have serene grace as its ability, then you get access to air slash and just flinch your way thru. In the end, Togekiss' rather low atk stat means that it will always be the best stat to reduce which means the best +spe nature is timid
