Vesting has to be looked at from two perspectives: as a tax event and as a golden handcuff. From a tax standpoint, there may be advantages to early vesting when the company valuation is lower. HOWEVER, you'll have to pay taxes this year on what may turn out to be worthless stock if your company goes under and then follow IRS schedule to recoup your losses over a number of years.
From a golden handcuffs standpoint, Vesting - especially 25% - does not make any sense to me and I doubt any sophisticated investor would allow it. Think about it this way: why is somebody rewarded with a 1/4 of a company which they can walk away with, when all they have done so far is helped to find a seed round. At least if you have started generating revenue or otherwise proven your business model, you can justify some vesting, but at this point, this is absolutely not a good idea.