des / les

Bonjour Roman,

-> you're using "les" because you're referring to liking flowers in general

Also, when using verbs of preference (such as aimer, adorer, détester, haïr, préférer), you must use le, la, l', or les. See the link below:

Using le, la, l', les before nouns when generalising (definite articles) 

 

-> you're talking about some unspecified flowers

Partitive articles and Definite articles

 

I hope this is helpful.

Bonne journée !