Yes it's very hot in April... especially in Bangkok...hv been to Phuket & Bkk in April....we used to escape the heat by spending the first half of the day mainly 11am to 3pm in the Malls...Weather gets better in the evenings... So if u plan ur days well, a holiday in April is manageable... And living in India, we are used to the hot Summers neways ☺
Early april is one of the best times to visit thailand. Of course it will be humid but you will find cheaper airfares and good hotel deals also . Choose Either Phuket or Krabi coz they are in the similar region .