I think it depends on what your needs really are. Personally, I do the software purchase (outright). My oldest does the membership on nearly all of her software. Her needs are more intensive and she does need to have access to the latest updates. If you find yourself wanting to purchase outright every time a new update is issued, then the membership would be the better choice.
I am not an Outlook fan, but it is our office's platform for emails/email management so it is a must have for me. However, your work may already have a subscription for that so I would check with IT. Most folks who do any work at home or check emails, usually get this perk from their employer. You could also check to see if your job already has a multi-user agreement with Microsoft that would allow you to use the programs you need. Another money saver is if you know a college student, they can get software on campus at the bookstore at a discount.