I use a 15" Macbook Pro Retina, my son has a 13" MacBookPro, and my wife uses a 15" MacBookPro. These are what I am most familiar with for baseline reference.
What phone do you use? What tablet are you thinking about? If either of them sport a fruit logo, get the corresponding laptop and enjoy a great deal of symmetry. The Next Gen OSX is going to
really integrate them all together through iCloud in way that makes it very convenient.
However, if you use an Android phone now, and are ambivalent about the tablet, Seriously look at the Microsoft Surface 3. I have been playing with one at work, and other than the resolution being smaller than I like, it's a pretty capable machine. It is a computer, not a tablet... but it's a tablet! It's somewhere between the Air and the 13" rMBP in size and weight, but has the benefits of tablet interface as well. I HATE Windows 8 on a desktop, but it works pretty darn well with the touch interface. The keyboard on the Surface 3 is definitely good enough as well. My boss was seemingly welded to his iPad and took it everywhere, but he lugged a Dell laptop around too, so that he could produce content such as complex spreadsheets and stuff. The iPad is amazing at many things, but mostly on the consumption side, not the production side of the data. He hated the laptop, but needed it still. Now with the Surface, he has taken 8lbs out of his bag, doubled his battery life, and has gone down to just the one device (plus his iPhone).
Now, if you are still leaning towards the Air, it is a fabulous device. The battery life is phenomenal, the screen is great, the keyboard is good, and the touchpad is the best in the industry. I run Parallels and Windows 7 on my rMBP and it's seamless. I have both OS's running concurrently, and its transparent to me which is which. Windows programs run in a dialog box, just like Mac programs. I can be knee deep in Excel in Windows, and get iMessage text windows popping up (Hugely convenient to text via computer by the way!). The issue of what OS to run becomes a non-issue. Just run them both.
Always always always buy as much RAM as you can. Especially on an Apple device where updating might not be possible (such as the RAM on the Air or rMBP).
I wouldn't recommend the 13" MacBookPro over the Air. If you need the better graphics power and CPU throughput, just get the 15" rMBP. Otherwise, stick with the Air. It's so much more conveniently sized and weighted.