Thanks thailand, I tried to explain the same thing but when I typed it out it just didn't look right for some reason...
So yeah ashes, like thailand says, if you're talking about the same wattage then the .5 is going to give you more, warmer vapor. But you can get as warm of a vape from the 1.5 as the .5 if you fiddle with the power, which is why it's so dependent on the settings. On the whole, I think the 1.5 will feel a little more comfortable as a starting point based on the things you were likely using on an eGo before now, though.
I'd say go with 3mg nic to start. You can always go up a bit. You can always go down, too, but 3mg is less likely to end in you feeling queasy. Honestly you may want to get a bottle of 0mg too, even a small one. I know when I got my first subtank it was so exciting I overdid it and I wish I had a bottle with no nic in it so I could have played without making myself ill.