Newbie w/first class airmiles question

My husband and I live in Greater London. We wish to visit Italy (will be our first time) for a week. No definitive destination yet, but will include Rome.

We've never used airmiles before.

I have 92,950 miles; husband has 12,741 miles.

With regard to return, first class tickets, my question is:

Would it be better from a cost-perspective to book first class reward tickets, or purchase coach tickets and use the airmiles to upgrade to first class.

Thank you.