Read the reviews section, listen to a few you-tubes on refilling, explore until you can't explore, then make a decision.
The difference in the devices is similar to your choice of a cigarette, a cigar, or a pipe.
The difference in flavors is similar to your choice of regular, menthol, or cloves.
There are 3 parts to an e-cig. The battery, the atomizer, and a container to hold fluid.
The 510 seems to be the most popular size.
They can look like a cigarette, but this restricts the size of the battery which may limit its use to a few hours before recharging.
The ego seems to be popular with a bigger battery and refillable cartomizers. A cartomizer is the atomizer and fluid container.
The ego-t is a tank that gets mixed reviews but is simple to refill and has a bit of maintenance to keep it running.
The go-go seems to be a new, well liked device but it's components are not interchangeable with other vendor's components.
Most (if not all of the vendors that list on this forum) are upstanding web-based merchants.
The mall kiosks and 7-11's are where you will get an overpriced, low-quality, product.
There will be a start-up cost of about the cost of a carton.
The ongoing costs will be about half the cost of a pack. Less as you learn more about DIY and refilling.
The public is the public. Some don't care, some do. The vapor disappears in a second, smoke lingers.
Many people can rebuttal my points because they have more experience than me. I only have 30 days of this to go on.
I did buy the overpriced garbage, then did my research, then bought an ego-T from cignot.com
I'm not disappointed with my decisions because what I have does work for me.
Could I have bought something better? Of course, but I stopped smoking immediately (with the overpriced garbage).
Good luck. Don't overwhelm yourself out of starting up.
...and welcome to the club.