designer and illustrator sketchbook are the best vector drawing. Sketchbook for assistance with layout and Illustrator is fantastic beyond description. Being adept primarily of vector graphics that I recommended!
Illustrator it is. I once had it, though I never got the chance to use it, now that my PC has been reformatted and the installer missing, I guess I'll grab one of those CS6 thingies Adobe has recently released.
There is a bit of a learning curve but once you get over that it is quite easy to use and canvas size limitations will be a thing of the past. On my 10 year old computer, with only 1GB of RAM, I managed to export an artwork which consisted of gradients, blurs and multiple semi-transparent objects to a whopping 27000x18000 pixels! That's the equivalent of 90x60 inch print at 300PPI/DPI (professional standard)! Granted, it took like half an hour to complete the process but, like I said, really old computer.
This isn't the most complex artwork that I've made using Inkscape, but here's a little something that I put together with it:
That comment coupled with your avatar looks of total shock.
But yeah, only 1GB, and no virtual RAM either. I'm not even going to tell you about the nearly 10 year old AMD Semprom 3000+ CPU and ATI Radeon 9000 GPU because it's just too embarrassing. Compared to a modern day Intel-i7, my CPU is 50x slower.
Ehhh don't worry about it, my PC is about to be (Or maybe IS) Obsolete. Though it is a bit better, I have a 2GB RAM with Nvidia GeForce 9300GE and an intel core duo2. I'm pretty sure inkscape (And that kind of project) Will go along in a faster rate.
I use Illustrator. I'm pretty happy with it, but at the same time I don't know much about other vector programs. I use it in school so that's what I'm used to.
If you want to actually be doing PAINTING the field is pretty tiny. The only vector package I can think of that was focused on simulating natural media was Creature House's Expression. Which Microsoft bought and killed at pretty much exactly the time I had the cashflow to get a copy.
That said, I've been using Illustrator for the past decade or so. You can do some pseudo-natural-media stuff with it, mostly by making lots of art brushes. And of course if you're not actually looking for a painterly look it excels in flat colors. I use it for pretty much all my work; I'm currently working on a graphic novel drawn entirely in it.