Recs.
Updated
SpecsUpdate
Pros
Pro Powerful computing for the size
A high end Surface Pro 4 does not disappoint on performance (except for the battery).
With the i7, 16GB RAM, and 256GB hard drive you can run Android Studio, Genymotion (running one VM), Virtual Box (running 1 VM), Chrome. Build times are reasonable, they are only slightly slower than a late-2011 MacBook Pro 15" (quad core).
Cons
Con Slightly awkward in your lap
This is a tablet with an attachable keyboard and adjustable "kickstand." It can be awkward using it resting in your lap. It's not great but it's also not as bad as you might expect. If you try it out in your lap before purchasing, you might find it to be stable. Because the kickstand rotates about 135 degrees you can use it in many seating positions. Again, it is still not quite as stable as a regular laptop so YMMV.
Con Poor to slightly-below-average battery life
When you give an ultraportable plenty of processing power, RAM, and a bright pixel dense display, it comes at a cost. When using this for development, the battery life is not great. It gets about 4 hours before it needs to charge. It does, however, charge fairly quickly.