It's funny, I'm a fair ways through my playthrough, and when I got to the split way back when my first thought was pretty much exactly the opposite of you. 'If I was in this situation I wouldn't even FLINCH about choosing Nohr, who in their right mind would choose Hoshido?'
I mean... The Nohr siblings are your FAMILY. Sure, there's no blood there, but family is really nothing to do with blood. These are the family you grew up with. Sure, it's really very apparent from the first few chapters that Garon is a massive arsehole. But the Nohr siblings aren't. Nohr as a nation isn't. Just it's ruler (Which admittedly does reflect really badly on Nohr as a nation). I'd take loving family over loving (and somewhat overbearing) strangers any day, even if Garon seems like a pretty bad egg, I found I had no real motivation to stay with Hoshido. The only people there that endeared themselves to me where the Queen and Takumi (The Queen for obvious reasons, Takumi because he had the most 'normal' reaction out of everyone.)
I admit, I was intending to play Conquest from the get go anyway, because long-time series fan and stuff, but I actually wanted to make the choice by the time the split came, too (And I got a bundle thing on it so I actually DID have the choice). Honestly, for a kingdom with a nasty king, you probably want as many nice princes & princesses as you can get your hands on, anyway. Many chapters in, I'd say I'm very happy with the siding with Nohr. (apart from the occasional really frustrating chapter).