the airbag system would allow for easiest ride adjustment, but it will totally kill the sporty feel of the car i think,... the aibag system just doesnt dampen like the gas shocks do... if you really need adjustment to stock height for winter and such, then yes, coilovers are probably the wy to go. get shocks while your at it becase if you lower it more than 1" your stock ones won't hold up too long...
although if you only need stock height in winter, i'd consider uying a spring/strut combo for lowering, and just swapping out the shock assembly for winter...