My advice to you is create a roadmap in terms of what you want your suspension to be. Say for example pick Bilstein, OME, Dobinson, ICON, FOX, Radflo, Ironman, Kings, Toytec, whatever suspension you like. It's probably easier to match the shock dampening characteristics of the front and rear if you stay with the same brand, but it's possible to match across brands (just more difficult).
Then just replace the front coilovers with your choice of brand. Make sure that the front is height adjustable, so that you can start with stock height to match your current stock rear airbags.
Then when you are ready to convert the rear, you can adjust the front (some front coilovers let you adjust without taking off the springs) to match your new rear coil conversion (assuming that you want a lift).
In terms of experience, I bought my GX470 already with the rear airbags tricked (raised about 1.25" by lowering the rear height sensors). So, I don't have experience with the rear air bags being left at stock height and only upgrading the front coilovers. With the tricked airbags, the ride feels stiffer in the rear (or harsh). The front Bilstein 6112s feel great and comfortable, but now I want to upgrade the front to 650 lbs/in coils since I have added weight in terms of skid plates, tow points, and sliders.