Prices current as of 2016.
13" MacBook Pro at $999:
Advantages: least expensive of this list, includes a DVD drive. RAM can be upgraded from 4 to 8 or 16GB (at a cost of about $60 or $100 respectively, as of Nov 2016).
Disadvantages: at 4.5 lbs, heaviest option on this list. Has spinning hard drive, which is not as fast as solid state drives on the other two options.
Ports: 2 USB, 1 Thunderbolt, 1 Firewire, 1 Ethernet, 1 SDXC card slot.
13" MacBook Air at $1149:
Advantages: very light, wedge-shape at 3lbs; uses solid state hard drive (vs. spinning hard drive on the above) to use less power and generate less heat.
Disadvantages: not the strongest processor, but if you're not doing graphic-intensive work you may not notice. No optical (DVD) drive. Needs adapter ($29) for wired network. Needs a different adapter ($29) for an external display. No HDMI port means you can't have both wired Ethernet + external display at the same time, as they'd both need the 1 Thunderbolt port. RAM upgrades only available upon special order at time of purchase, not after purchase.
Ports: 2 USB, 1 Thunderbolt, 1 SDXC card slot.
mid-range 13" MacBook Pro Retina at $1399:
Advantages: Good processor, high resolution. Lighter than traditional MacBook Pro (3.5 vs 4.5 lbs).
Disadvantages: higher price, no optical (DVD) drive. Needs adapter ($29) for wired network. May need video adapter ($29) if not using HDMI port. RAM upgrades only available upon special order at time of purchase, not after purchase.
Ports: 2 USB, 2 Thunderbolt, 1 HDMI, 1 SDXC card slot.
Add $183 for Applecare for any of these.
For the MBP, it is recommended to purchase 2x 8GB RAM chips to upgrade from the standard 2x 2GB (price in Nov. 2016 was $50/8GB chip). The MBA and MBP-Retina may be ordered with upgrades as well for RAM, storage, or processor, depending on model -- though it can add time until delivery as they are special orders.