Whether it is better or depends on:
- the tax costs or benefits of selling assets
- the possibly greater cost of your time in choosing which assets to sell etc, vs just directing new contributions to the underweight asset
- the friction of paying the costs (fees, spread, brokerage etc) of two transactions (sell-buy)
My feeling is that generally you not sell but rather just redirect new contributions, unless that is not going to bring you back in balance within a reasonable time frame, or there is some other compelling reason to change.
As you're currently contributing 7.5% of your portfolio value every year it seems likely that you will be able to rebalance using contributions alone. (If you were older and were contributing only 1% of your portfolio value every year that would probably not be enough.)
One compelling reason to change would be a tax benefit. Another is that you may have decided you no longer like one investment provider (eg high fees, whatever) and you are going to take the opportunity of moving away from them to rebalance.
You could say that if any asset class is more than say 10% higher than it should be, you will sell; otherwise just redirect new contributions.