It truly is a question of lifestyle, as mentioned by Ines. In South Beach you will find more restaurants, shopping and nightlife than in Sunny Isles. However, with that, you get more people and more traffic. It is tolerable, but very different than 'Sleepy Sunny Isles'. Also you do not mention what you are looking to buy, whether a home or a condo??? and price range??? live year-round or just a few weeks???
At the end of the day they are both great places to be.
The only way to know the answer to that question is to ask:
1) Is this for your own living or for investment?
2) Are you talking about condo, townhouse, or single family?
3) What price range are you in
4) What are the most important things to you in terms of the neighborhood/lifestyle?
I'll be glad to discuss it further with you.. just give me a call.
I live and work in Sunny Isles Beach and love to visit SoBe every so often. Fortunately, I'm always able to nagivate my way back to Sunny Isles before daybreak- but,... in the event that one day I'd be unable to... it would be good to have a nest to call home.