With an examination of the two sentences simply as they are written here, the first one has a predicate that is more complete in idea since the second sentence seems unfinished because the reader expects a time phrase at the end. For, the use of the Present tense, Basic Form, appears here to denote a recurring action. "We arrange to meet for lunch"; however, the reader does not know when. Perhaps, then, one could finish this sentence in this way,
We arrange to meet for lunch whenever I am in town.
So, if the word clear means clarity of meaning, then #1 contains a clearer verb.
It is noteworthy, though, to remember that in speaking and in writing, it is always advisable to use Active, rather than Passive Voice. And, of course, the predicate of the first sentence contains a verb phrase that demonstrates Passive Voice. Therefore, IF it is possible to revise either of these sentences, perhaps the student can rewrite #2, which is in Active Voice as suggested above, or in this manner,
We have arranged to meet for lunch.
Employing the Present Perfect tense, rather than the simple Present tense ["simple" as in one verb], there is a completeness to the sentence and, thus, more clarity than in #1 as it is written.