If the keyboard is a prime consideration, I almost prefer the MBP keyboards over the AlBooks, although there's little practical difference in them and they're both excellent.
I wrote the bulk of my master's thesis on an MBP 4,1 where most of the keycaps had been worn through-evidently I wasn't the first person to type a lot on it
The 3,1 and 4,1 offer you a great range of OS X compatiblity-among the best of any modern Mac. The 4,1 officially supports 10.5 to 10.11, and it's only a small amount of work to extend that back to 10.4 as well as forward I think to 10.13(I haven't followed terribly closely). The 15" models all have more or less the same resolution as the DLSD, and on the 3,1 and 4,1 I think they're all LED backlit. On a 17", a 1920x1200 screen with LED backlights was an option, although they're not too difficult to find.
The GPUs on most are a ticking time bomb, but
@dosdude1 can fix that permanently.
Add a USB 3.0 Expresscard and you have USB 3.0 in 10.7 and newer.
An SSD will usually make them fly, and you don't really even need to spend a fortune or deal with work-arounds since these are SATA native. I'm fixing up an MBP 8,2 for someone at work to give to her grand-daughter, and picked up a 240gb PNY brand drive at Best Buy yesterday for $30. I wouldn't necessarily use that drive in one of my beat-on-12-hours-a-day computers(I stick with Samsung Evos) but it will work fine for this application.