Core i7 should be your choice.

AFAIK and last I checked, AMD doesn't have their s4 together again yet. At some point, I'm sure they'll leapfrog Intel again when the big guys get complacent, but that ain't yet.

Core i3 = dual core + HT, i5 = quad core, i7 = quad core + HT, bigger cache.

HT = hyper-threading = 2 threads per core. Quad core without HT is faster than dual-core with HT because hyperthreading shares resources on the same core.

Regardless of brand, I'd grab something like this, except with 16GB and a 1080p screen (or better) if you can.

(I'm still partial to Dell, so I picked one of theirs, but I'm not advocating a brand. And yes, I picked a Windows 7 example on purpose. Windows 8 = evil.)

Performance-wise I'd get something with an SSD. Mechanical hard drives are just too slow for the type of work you'll be doing, and laptop drives are slower than desktop drives (and generate more heat, and tend to last shorter before dying). SSDs generate little or no heat and last just as long, if not longer. Detail: With an SSD, longevity comes from minimizing writes, so turning things off like swapfile, indexing, etc greatly helps, and to a certain limited extent, you have control over how long the drive lasts. With a mechanical drive, as long as it's running, it's generating heat...and a laptop is far less able to shed that than a desktop. Also, an SSD draws less power, so you'll likely save more than enough battery usage to afford to have the extra RAM.