This probably won't apply to you, but on "short" flights on Horizon you can't get soda, only juice. I am at a loss as to what a "short" flight is. I experienced this kind of beverage service going from EUG to SEA last summer. EUG to SEA is one hour. One-hour flights on other airlines have full beverage service. Perhaps the rule is based on flight distance, as EUG to SEA is under 250 nm.
The Q400 goes a little slower than the CRJ. Still 5x faster than driving (at least on EUG-SEA).
I've flown on both the Q400 and CRJ700 (though the CRJ was on Skywest, not Horizon), and both seem about the same in width. However, according to Seatguru.com, the Q400 has wider seats. Legroom in any regional aircraft will feel cramped. I haven't been in the lavatory on the Q400, but the lavatory on the CRJ700 is a little uncomfortable. Due to the sloping ceiling near the actual toilet, urinating standing up if you're around 6 feet tall will be a little difficult-you either have to stand 2 feet back or "do your business" sitting down. Too much information, yet true.
The Q400 is pretty quiet but you can feel everything vibrating throughout the whole flight. The CRJ700 is deafiningly loud on takeoff.