I would go with the firecore over the msd for "plug and play", mainly because of price, I had an msd plug and play, it was used when I got it and it still worked when i sold the car, and I see the new owner who has never mentioned a problem, I bought it used for $150...
Now for the motor I am putting in my 440-6 I bought a spanking new msd 8546 for $255 (fleabay) and a new msd 6425 for $150 (also fleabay), both new and unused... I see deals for the ready to runs too, just look around.. As for the best price, amazon, summit, jegs, all pretty much the same, although with amazon if you sign up for a chase, citi, or what ever credit card they are pushing now you can get $50-$100 off of the distributor with the first purchase, besides something like that, I dont see any savings(and now that amazon charges tax, the cc savings is useless...)...
good luck..