228. I own a 229, but it's a .40.
Here's why: I like capacity and concealability. My favorite guns are midsized guns (ie, Glock 23, Walther P99, Para-Ord P13.45) because you generally give up 2 rounds of capacity for added concealability. But, they are much easier to carry, particularly for someone 5 foot 7 (ie, me).
I'd knock out the 225 because I'd rather carry 13 rounds than 7. I'd knock out the 226 because while I'd rather carry 15 rounds than 13 rounds, the 228 is much more concealable, and therefore I would be more likely to carry it more often.
Keep in mind that this is not the right choice for everyone. Those with big hands might want the 226, while others with particularly small hands might want the 225. Also, some people might not like hi-cap guns, and others might just like the feel of one or the other. If there was one gun that was the best, Sig wouldn't be making more than one model, would they?