Praia do Guincho is probably the best big air spot in Porgutal, but beware, it is a very difficult spot: the wind is always stronger in Guincho compared to other nearby spots, because of the cliffs along the coast and the venturi effect. Do no mistake, riding there can be tricky: there are rocks in the middle of the spot and rocks downwind. Make sure you know what you're doing.
Praia Nova Vaga and Praia Bela Vista are two spots on the Costa da Caparica, these are very nice for big air and provide nice waves as kickers, the wind usually "lifts" more in Costa da Caparica than in other spots, except for Guincho. In summer as there are many swimmers and the beach lifeguards whistle at you to move out. The wind usually lifts really well here.
Costa de Lavos in central Portugal is definitely a very good Big Air spot with strong winds and extremely nice wave kickers.