Tips for 25 words or less competition?

The "but" sounds better in the sense that I think another "and" would be one times too many for one sentence. Still, I think it would be better if you used the word "yet" instead of either of those. Also, you could squeeze in another word if you contracted "it is" to "it's". In that case, I would recommend, "__ is my favourite Pokemon because it's adorable and endearing in both personality and appearance, yet powerful at the same time." (I chose adorable instead of cute because it sounds a little fuller with the word endearing after it). You can use none, one, or any of my suggestions however you like. Good luck, I hope you win! ^_^