It all boils down to what do each of you (each member of your startup team) want to accomplish by awarding/obtaining equity? Equity is an investment in the future of the company. How important is it for each individual to be invested?
You mentioned "depending on ... the success of the startup". The value of any equity is completely dependent on the success of the startup. Once there is a track record of success, the equity is (at least in theory) worth more - so an individual would receive less equity (as a % of the enterprise) for the same contribution.
If a goal the equity award is to increase commitment, then having equity might motivate the individual to do everything personally possible to support success. That might factor into your equity strategy.
It's often useful to think about equity (an investment in the future of the company) separately from pay (compensation for the market value of the goods and service provided). If you could pay your partners in cash, would they use that cash to purchase the equity you are offering? Answering that question might give each of you some perspective on the personal value and desirability of equity.
I admire your decision to award equity based on performance, not simply a time-based vesting scheme. It's usually the fairest option. Then there are the matters of dilution and liquidation ... both issues that can touch on perceived fairness, future (monetary) investor participation, and legal/contract issues.
We (my consulting firm and our clients) usually find that having honest, open, and often difficult conversations "while we're still friends" (and as early as possible in the process) then using contracts to document those common understandings (rather than to try to gain some kind of upper hand) is the best approach. Unfortunately too few founding teams bother to make the effort.
Thanks for caring enough to at least ask the question.