Any particular reason you're thinking Malaysia? I would recommend Vietnam or Thailand a thousand times more as a destination than Malaysia, for beaches and for enjoyment.
Penang is Costa Del Anywhere, it feels just like any beach destination in the Med in a lot of ways. We went there as part of our honeymoon and regretted it big time. Really don't have a good word to say about it, hotel was dated, restaurants weren't great around the place.
Friends went to Langkawi and raved about it.