Hard to say which is the best one, but there could be one which suits your research focus. The following is summed up by Partington, A. (1998). Patterns and meanings: Using corpora for English language research and teaching. Amsterdam: John Benjamins.
Meaning by collocation is an abstraction at the syntagmatic level and is not directly concerned with the conceptual or idea approach to the meaning of words. (Firth, 1957, 196)
Collocation is the occurrence of two or more words within a short space of each other in a text. (Sinclair, 1991, 170)
Psychological or associative definition:
Collocative meaning consists of the associations a word acquires on account of the meanings of words which tend to occur in its environment. (Leech, 1974, 20)
Collocation has long been the name given to the relationship a lexical item has with items that appear with greater than random probability in its (textual) context. (Hoey, 1991, 6-7)
Collocation refers to a group of two or more words that usually go together. A good way to think of collocation is to look at the word collocation. Co - meaning together - location - meaning place. Collocation are words that are located together. All the best!