You're a Roman. This entitles you to attacking who you want, when you want, where you want, etc


But if you mean strategically... Well, the Spaniards seemed fairly easy to conquer when I played as the Julii, plus the territories that way give you better leverage with Naval warfare. The Germans are good targets too since you'll get to smash those uncouth Britons once you've worked your way north a bit. Then you'll have a nice big red splotch on your mini-map to admire.

Enough hand wringing! More teeth smashing violence!

Have fun, bonne chance!