I like both and have had both, even all at the same time, as you can see in my avatar. As far as hiking, I live in a hiking heaven in north Idaho and my little Chihuahuas have always hiked with me when I had my Lab and Doberman. Some of those hikes were all day hikes upwards of 9 or 10 miles through the woods. The Chi's could at times run circles around the bigger dogs and were more adept at circumventing obstacles such as downed trees that had branches all over the place. They're very manuverable and agile and can fit through small places. When they run fast, they're a blur. So stamina in large part is dependent on conditioning.
At my age now, I like dogs I can pick up easily. And like it was said, I don't trip over them because unlike my larger dogs, they take it as a big responsibility for themselves to watch out and they scamper right out of the way in a heart beat whenever I'm moving around. My bigger dogs would just stand there like, "duh..." until I told them, "excuse me."
As far as barking, Chihuahuas are notorious yappers. But that's because a lot of people don't teach their dogs. Mine only bark when someone comes to the door or for some other thing they hear outside which alarms them. And they are rather easily alarmed and have very keen hearing. (great watch dogs) It is rather high pitched but it's not as loud as Toker's. She has a very loud, sharp bark that makes me jump out of my skin. I can get Jose` to bark on cue and they both stop when I tell them, "enough." So, the barking is not much of a problem. Training, IMO, a cued bark and a cued "quiet" or "enough" is essential but that goes for any dog that barks a lot.
Most of the points were already made such as ease with traveling, bathing etc. They're clean, not too hairy (the smooth coated Chi's or other breeds). They're cozy enough to sleep with without hogging the bed. There are all kinds of reasons small dogs appeal to me even though I also like big dogs, but for my life style now-a-days, I will probably stick with small dogs, depending on breed of course. I like Poodles, Chi's and other breeds which are quite dependent, like Giny was saying. That's probably why I loved my Doberman too....exceedingly enthralled with me. LOL.