+1 Neither is really going to strengthen your credit profile. Tweaking revolving utilization is something that can be done just prior to applying for new credit, requesting CLi's, etc. Your revolving utilization is determined based on the balances and limits as currently indicated in your reports. Prior balances and limits are irrelevant so there's no long term benefit from fretting over it.
Making purchases each month and PIF'ing doesn't really matter either. PIF'ing is beneficial in avoiding accumulation of revovling debt and to avoid incurring interest so there is benefit there. Using your accounts prevents them form being closed due to inactivity but that really doesn't matter for profile building.
Look at the standard FICO scoring factors:
http://www.myfico.com/crediteducation/whatsinyourscore.aspx
Payment History is really just a matter of whether or not your payments are on time. It really doesn't care if you PIF or not. It's about whether or not you're making at least the minimum by the due date.
Where amount matters is Amounts Owed and for revolving credit accounts it's revovling utilization that matters. Balance to loan ratio for your installments also matters for Amounts Owed but it does not have anywhere near the same impact as revolving utilization.
Length of Credit History is mostly about your Average Age of Accounts.
Credit Mix is about the variety of credit accounts that you have.
New Credit is where hard pulls and having new accounts on your reports factor in.
If you want to strengthen your credit profile then always pay on time. Keep your revolving utilization in check. Build your AAoA but at the same time thicken your credit profile by adding new accounts as your financial needs dictate and your credit profile allows. There's a balance to strike there which is why spreeing and gardening is generally a poor idea IMO. Building your credit profile is a long, slow process. Time and responsible maangement of your credit accounts and finances are what it's going to take.
