The Pico. It's small (photos don't make it justice, hold it in your hand and marvel), ergonomic and well built. Good buttons, bright display, nice sleek design. It's the one mod I always recommend to beginners who want to step up from pen styles. The TC mode works great albeit is as always a battery drainer. You might want to bring a spare battery especially if you vape at higher watts. If I absolutely must mention a con it's the way the battery case hinders you from putting atomizers thick services than 22 on. I've seen people modding it by filing it down so I don't get why eLeaf made it so fat. 24mm atomizers are becoming more and more common today.
I can't recommend Pico enough. Whether it's for a small side-mod or you want a small single battery mod as your main you can't go wrong!