Definitely an excursion is also highly recommended to visit Valencia.
–BUS: The company Alsa joins every two hours approximately Alicante with Valencia : www.alsa.es
When you buy your ticket remember that by motorway the journey takes 2 and a half hours, and by national road can be up to 4 hours.
By bus you can go to Valencia from the most important destinations of the north of the province of Alicante: Benidorm, Altea, Calpe, Denia …
Only from Alicante city. It is a highly recommended option because the journey time is usually 1h. and a half. Check the schedules and prices, and buy your ticket in www.renfe.es