Spain is by far the harder faction than Numidia IMO. For one reason only... Rome. The hardest enemy for Spain is not the Gauls, but the Julii. The Romans always invade with general armies making them hard to bribe. Also the hastati are a hell of a lot toughter than warbands, your roundshields can't hope to take on hastati even with repeated charges, those Roman bastasrds just stand up too well to it. Another point that makes the Julii hard to fight is where you fight them at. Since they always land at Osca, you have a hard time reinforcing and retraining your men cause Osca is so underdeveloped and grows slowly.

With the Numidians, you can make peace with Carthage and keep it so you only have to worry about Egypt. The Spanish threat is little cause they bring so few troops and your light armies can take them on no problem in the desert where you have the natural advantage. The Egyptian chariot archers are a pain but with enough light infantry (i.e. skirmishers) You can hold you own.