I googled the above 2 cities, here is what is on TravelAdvisor,
of course it's just someone's personal opinion.
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1. Re: Valencia, Alicante or Marbella?
As for safety, I don´t think you would have any problems in any of the three cities. None of the three cities you´re interested in are the size of your hometown
London. As long as you use your common sense, as you would do at home,
Spain is a very safe country.
If you´re looking for a piece of real Spain I´d go for
Valencia or possibly
Alicante, definitely not
Marbella. Marbella is full of hotels and restaurants catering to foreign tourists. It´s a personal opinion, but I think Marbella hardly has anything interesting to offer.
Alicante is a nice, small city. Quite touristy in summer, with great beaches. Valencia has more to offer culturally speaking, as it is bigger. Nice beaches too. In my opinion, Valencia is your best bet.
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2. Re: Valencia, Alicante or Marbella?
No contest,
Valencia every time. Lovely city with plenty to do and has a beach.
Alicante is OK, but a small city.
Marbella is tacky and certainly lacks the glitz it once had. It is also very expensive.