I def wouldnt get a slim ecig (one that looks like a real cig) bc they have small batteries that need to be recharged very frequently.
Check out the E-Power and kGo. Their both quality PVs that give a great vape and have very good battery life. The eGo is also popular, but personally I think the E-Power and kGo are both def better than the eGo. The eGo is only 3.3-3.4V, while the E-Power and kGo are both 3.7V PVs. The 3.7V PVs provide alittle more "oomph", and more importantly they handle the lower resistnace attys and cartos a lot better.
I have an E-Power and love it. The main difference between the E-Power and kGo is that the E-Power uses non-proprietary batteries, which are removable. E-Power batteries cost $4-5 compared to eGo/kGo batteries that cost $14-20. The batteries are 1050mah so they last a long time and I get on avg a day to a day and a half on one battery. Also I find it much easier to carry a spare battery with the E-power. The batteries are small, about the size of a AA but alittle longer, so its easy to carry a spare in your pocket or bag, and if needed, uscrew the switch and pop in a fresh battery. With the eGo and kGo, to carry a spare battery you have no choice but to carry a second PV with you since the battery is inside of the unit. Also everything is replaceable on the E-Power so its cheaper to maintain.
The kGo is also a nice PV, even though it uses proprietary batteries. The batteries are 1100mah so they last a long time as well, and most people can get a full day out of one battery.
I think youd be really happy with an E-Power or kGo. They both have 510 connections, which is the most popular threading, so youll have many options for different attys and cartos you could use.
Both units have awesome battery life, and really arnt as big as they look in pictures. I easily carry my E-Power in my pocket with me everywhere I go.
Heres a picture of my E-Powers to give you a better idea of how big they are:

I use 3.5ml tanks on my E-Power, but you can also just use regular cartos without the tanks. I really like the 3.5ml tanks though bc their perfect for E-power/kGo sized PVs and they really dont make the PV much bigger, but at the same time allow you to go for a lot longer without needing to refill.
I fill my tanks and pop in a fresh battery every morning before I go to work and I can easily vape all day completely maintanence free