New

i would probably say brettonians, it isnt that hard to learn their play style and if you go all knights then you will have a low model count in your amry so it would probably be easier on the wallet lol.

that being said, i would recommend you look at the army selector, see what interests you in the ways of play style then decide, cause when it comes down to it, if you dont like how the army plays you wont really have much fun.

I agree with grungni about the bretts being cheap money wise and all but if you don't like the feel of them I recomend going lizardmen. They are a great army for beginners and as long as you don't make an all skink army it should be pretty cheap.