There's no right answer, it depends on what you want to find.
You can search for keywords on Heepsy:
If you search for one keyword at the time, you will be shown all the profiles that use that keyword (they could include more keywords).
If you search for two or more separate keywords at the same time, Heepsy will show you profiles that use at least one of those keywords.
If you search for a keyword that includes more than one word, you will see the profiles that use all of those keywords.
So if you want a more specific search, use multiple keywords together. If you want to see broader results, search one keyword at a time or several keywords separetely.