I am taking this as your question- repeated phrases or different phrases with the same meaning.
I am going to take a side-trip, but bare with me- I am sure we will arrive at the right place. The reason is, I am not sure you understand the basics of SEO well enough. So please humor me. It will make sense in the end.
When you talk about SEO, you really are talking about a few basic things to start. Links,
h1 header tags,
description meta-tag, and content.
Keyword density is a myth. Repeating the same word is not SEO. Instead knowing where and how to use keywords is. If you follow a trail from the link through the page, here is what you should see. Use your few most important keywords in the link,
title tag, and
H1 tag. Then your few lessor important keywords in your
description meta-tag and
h1 and possibly
h2 header tags. Then the pages content should use all keywords. This is just a quick rundown. But I hope that you are getting my point. You can reuse keywords in appropriate ways through your mark-up and content, but not repeated in such as way as to be keyword loading.
Now to answer your question. You can and should use synonyms. That works and can be used as your secondary few keywords. In fact, it is highly recommended within content.
I like the first scenario, but with a bit of a caveat. It allows you to have a predictable and structured set of keywords that your site/pages can rank for and you know how to use. It fits the model of SEO I just gave and a database of terms, synonyms, and term relationships can help you to build rank for keywords in a consistent and predictable way.
Now for the caveat. I also like the second scenario too. It can allow for uniqueness and flexibility. If a user can add information to supplement the set of keywords, that can add value and uniqueness that would prevent pages from being too keyword heavy. I can also possible be used for the
description meta-tag which does not add weight for keywords.
Now I know that this is not a complete model, but perhaps it will help you to get your creative juices flowing. I expect follow-up questions and ideas will come to mind.
There you have it- a split decision from the judges! Option one wins on a technicality! But the crowd shouts fowl!