I have also used a percentage of the total, net lease value and found it to be the most effective. As an example, if the rent on a 12 month lease is $1000, and the agent gives away a half a month in free rent, the total value of the contract is $11,500. 1% commission is $115.00, of which half should go to the leasing agent, and the other half split among the remaining team members.
The real money is made with the lease renewal and increasing the rent for the next rental term without losing the resident. Lease renewal bonuses should always be higher than new lease commissions to encourage great resident service throughout the lease term. 1.5% of the value of the contract is a great renewal incentive. Using the amount above, if the rent increases by $25 per month, the value of the new contract is $12,300, and the renewal incentive is $185. While this is slightly more than the total of the rent increase, there is no vacancy loss or turnover cost, making this a very attractive option to both the employee and the owner. In this situation, the renewal incentive is split among the employees involved with the renewal, usually the assistant manager and the maintenance team.
Personally, I think managers should be incentivized separately and should not share in the leasing or renewal commissions, unless the property is small and the manager also actively leases and processes renewals as part of their normal workday responsibilities.