As we all know, mobile platforms and the Nintendo 3DS are both on-the-go devices. They each offer games, and, at first glance, 3DS is most likely better for gaming due to it being a dedicated game device. However, there are pros and cons to each.
Expenses: Both can be expensive depending on extraneous factors like a cell provider or the complements to these items (chargers, cases, etc). In the long run, the 3DS is more expensive because of games' prices. Mobile games are ten dollars at most, 3DS games thirty.
Games: 3DS developers have the better chance to make more story-oriented games. Mobile games are more quick stress-relievers: Games like Paper Toss and Flappy Bird have no goal or way of beating the game, you just complete different levels and quick matches.
Audience: For hardcore gamers, the 3DS is definitely the answer because the games are of higher quality and depth. Battery life for any phone won't last too long on a game, especially depending on how heated your phone will get and how much storage is being taken up. Think about the time that Pokémon Go Fest failed miserably because of too many players on the server. 3DS is where you’ll find more people to hang out and play with.
Your preference for the 3DS or mobile platforms depends on what you’re looking for in a game and the time you invest in them. When you’re feeling for a light, quick game, mobile is the answer. But if you want a long-lasting game, or you’re ready to game for hours on end, the 3DS is better.
Most of the big titles are not on mobile, only spin-offs such as Magikarp Jump are. Also take into consideration that you can download emulators on mobile devices, though it is often too much for heat capacity and battery life, leading to glitching and an overall annoying experience.
Image from playbrains.com