Here's my thought on this whole situation (yeah, I know, I'm coming into this a little late in the conversation):
I started with a cigarette-sized unit like many of us do. Within a week or two, I'd picked up an ego (which is, sizewise, the same as the kgo/Riva type of batteries). I still use those batteries with different stuff on top than what they originally came with, because they have 510 threading and thus are usable with a lot of different options.
I highly recommend kgo or Riva batteries over ego batteries. This is because the kgo/Riva batteries are a true 3.7 volt battery, whereas ego batteries are protected and produce about 3.4 volts, and I found that the majority of the juices I use taste better at that slightly higher voltage. I also have a variable voltage mod, and there are some liquids I use that are even better at higher voltages still, but to be honest, I could, and do, still vape them on occasion on the ego/Riva/kgo-type batteries.
I recommend using cartomizers rather than the atomizers if you're on the go, and the primary reason for this is convenience. If I have to add drops constantly, it becomes frustrating. Cartomizers last me longer than an atomizer does, as they hold more liquid. If you find after use that you still need to carry a bottle around with you to refill a cartomizer (because this can happen), you can at that time consider getting yourself a punched cartomizer with an external tank (sometimes called a carto-tank), and the external tanks that are available out there hold between 3-6ml of liquid. That, combined with what the cartomizer itself holds (usually at least 1-1.5ml), is more than enough for me even on a really heavy vaping day.
What I presently like to use the most, and what I think I'm going to be using the most for a very long time, is carto-tanks on either kgo/Riva batteries or on my variable voltage mod. As all of the above are 510-threaded, it means that I can switch my tanks to whatever battery I want to use at the time, depending on what size equipment I want to carry with me. If I'm going to be out and about and want to stick it in my jeans pocket, I tend to go with a kgo or Riva battery (they have the option of pushing the button three to five times to set it in an "off" mode so it doesn't accidentally fire in my pocket) with my tank on top, and voila, I actually am using less space in my pocket than a lighter and a pack of cigarettes would've taken, and I have at least 3ml of liquid to vape on a battery that'll hold up for a lot longer than the smaller size batteries would have.
What you put on top, in other words, is entirely up to you. I have atomizers for dripping, not that I use them much. I have non-punched, standard cartomizers that I use on occasion for flavors that I want less. Similarly, I have small clearomizers (effectively a miniature tank with some wicking material) that I use for smaller doses of certain flavors (I just can't vape key lime pie all day, no matter how hard I try). I have punched cartomizers with tanks for the flavors I like the most and that I vape the most of. All of the above work with everything else that I have, so if I decide to switch it up, I can.
So to put this all into a simple sentence: pick a threading size (I recommend 510 threading because it's the most versatile at present), pick a battery to start with (I do recommend that kgo you're looking at for simplicity and portability), and pick up a couple standard cartomizers to start out with. Then go from there in small bursts as you feel like experimenting with other options. When you find something you absolutely love to use that provides what you like in terms of flavor and experience, stick with it as your primary option, but don't be afraid to experiment a little when you have the cash to do so, because there's new stuff coming out all the time now and you're not stuck with one particular type of unit or option anymore.
Hope that helps a bit!
. I only suggested keeping them far apart as the two chargers look similar and I know I would eventually plug in the wrong configuration and possibly see that ever dreaded puff of white electronics smoke escape.
