I've traveled to cities all around the world but N.Y was the most special because I met you there.
I've been to many cities all over the world but N.Y is still my favorite place because that's where I met you.
1) I've traveled to cities all around the world but N.Y was the most special because I met you there.
「世界中の都市を旅行したけど、あなたに出会ったニューヨークが一番特別です。」
the most special で「一番特別」
2) I've been to many cities all over the world but N.Y is still my favorite place because that's where we met.
「世界中のたくさんの都市に行ったけど、私たちが出会ったニューヨークは私のお気に入りの場所です。」
my favorite place で「お気に入りの場所・大好きな場所」
「今まで（世界中の）たくさんの都市を旅行しました。」は
I've traveled to cities all around the world. や
I've been to many cities all over the world.
と言えます。
ご参考になれば幸いです！
日本 
