Welcome to VT. Since you are looking for a small pv, I would suggest a volt from smokelessimage. A lot of us use the Ego, but it is a little bigger than an analog, the battery last longer. The volt has a PCC you can buy to charge it on the go and they sell blank cartos or prefilled ones. The prefilled ones never taste as good as when you fill your own and it is not a hassle at all to do that. There is a newbie section on the forum that will show you how to do that, watch some videos.
The juice is not messy and should not leak out of the carto. After filled, you do have to top off every hour or so depending on how much you vape. You could prefill a few, but a small case that fits your PCC and a bottle of juice is really all you need for out and about.
There is also a 510 that is small but the battery life is not as good. Most people get about 1 to 2 hours on it, so you need to have several batteries. I get about 4 to 5 hours on the volt when I use it, so you still need more than one battery, you charge one while you vape the other.
Hope this helps a little.