As I might have noted in this post, the dragon type can be a challenging one to master at first, partly because of the general temperament of the members of this element, partly because of their sheer rarity, partly because they grow at a somewhat slower rate than most other pokémon, and partly because some dragon-types are actually rather difficult to train due to physical limitations. For example, dratini can only learn a handful of weak moves (most notably Wrap) until it advances in age. Goomy, for another example, learn a wide variety of moves, but it must be kept in a moist environment at all times and thus can only really battle in pools, marshlands, or other largely wet battlefields. Deino, for a last example, is both strong and has few physical limitations that keep it from being a valuable member of your team, but it’s highly aggressive and liable to refuse orders when given them.
The others are by and large easier to train; it’s just a matter of finding them in the first place. For example, jangmo-o is an excellent battler, but it is only found in one specific part of one specific mountain on one specific island in the region of Alola. Likewise, noibat are only found in specific caves around the world, and axew, although it’s a popular starter pokémon among dragon-type fans, really only live in three other specific caves, separate from noibat habitats.
This means that of all of the dragon pokémon, really bagon and gible are your best choices, as they are fairly reasonable to train, eager to fight for a human (or otherwise grow towards evolution, in bagon’s case), and are far, far less painful to find. Granted, of course, this doesn’t mean that you can’t ever try to train the others. Really, all dragons can grow to be wonderful, powerful members of a team if given enough patience. It’s just that bagon and gible require less patience than others.
The Pokédex According to Bill 