You would say "Watashi no tomodachi ga suki desu." There are many ways of saying "my" and friend. But the end part of the sentence "ga suki desu" is always said the same way.

Of course you like your friend. If he's your friend, you automatically like him. The sentence is strange.

you can say, [ watashi wa tomodachi ga suki desu / 私は友達が好きです。 /わたしはともだちがすきです　] は is pronouced wa) in [ watashi wa ] . followed by subject, は is pronounce as WA.