You can't compare the two .... one's in Town on a hillside facing the sea, the other is at a beach area, right on the beach. Two completely different styles of hotel. To choose between them you have to compare what each offers and see which one best suits your personal tastes and preferences.
I recommend Hotel Poseidon. It's a ten minute walk into the main town, perched a bit up on a hill, with gorgeous views of the 3 windmills and the bay. There is a small beach adjacent to the property and the pool is heavenly. The people are
wonderful and it is totally updated. If you can go a bit later in September, the hotel prices will drop after about the 12th or 15th, and the weather is still great.
Poseidon won't be found on a lot of big name travel sites, but they do have a website you can google or better yet, use a travel agent (I can recommend a good one if you want to private message me on here) to plan your whole trip.
I agree with the other poster who said don't rent an ATV. When I was there, I saw countless people with arm and leg injuries from riding them. I don't think you even need a car if you stay in/near town; buses are easy and available.
I prefer a hotel in the Beach.
I have read that at cavo the cheapest rooms that I can pay don't value the money and are noisy.
Juliana if staying at the beach is your priority then choose the Branco its right on it plus its close to 4 other beaches by foot. Regarding the Poseidon it is on booking.com and is located in a good position close to town and the bus station. The small beach adjacent to the hotel is not imo the sort to sit on or swim at there are so many other better beaches to do this on though it is a nice spot to view the famous Mykonos sunset from
Since you prefer a beach hotel I'm surprised you were asking for advice between Branco and Cavo Tagoo.
There are other beachfront hotels besides Branco at Platis Gialos, including Thalassa Boutique, Mykonos Palace & its luxury wing the Mykonos Dove, Acrogiali, and Kosmoplatz. While not on the beachfront, Petinos Beach Hotel overlooks the beach, and is only a few steps away from it.
we needed up not booking a hotel yet and still need some help. Our friends stayed at Adrinokos hotel and loved it. What are your thoughts: we are only there for 3 nights I really just want a hotel that has a hot tub so we can relax a bit in the afternoon then go out to some clubs. Thanks for your help!!
Great hotel rooms and facilities since their renovations & upgrade more than 5 years ago, and great staff. There weren't any outdoor jacuzzis when we were shown a variety of rooms and suites but apparently they have added some to several junior suites for this year.
Only thing I don't like about the hotel it its location,since you have to cross the very busy ring road to get to & from Mykonos Town. It's not well-placed for easy access to clubs etc.
But if you want it mainly for that hot tub, go for it.