If you're not sure which one to buy, why don't you buy both?
If you can't decide which one you like better, just get them both.
ーIf you're not sure which one to buy, why don't you buy both?
「どっちを買うかわからないなら、両方買ったら？」
why don't you ...? で「…してはどうですか？」
to buy both で「両方買う」
ーIf you can't decide which one you like better, just get them both.
「どっちが好きか決められないなら、両方買っちゃいなよ」
can't decide で「決められない」
to get them both で「両方買う」
ご参考まで！
カナダ 
