I don't know about 'the Best', but Autozone has decent priced engines
(assembled in Mexico) with a 3 year unlimited mileage warranty. I put a 318
complete Long Block in my 87 4x4 pickup last year and was well pleased with
the motor for $1000. Advanced Auto (two blocks from AZ) had a similiar
engine/warranty package but my buddy at AZ  guanteened he would beat any
Advanced price by $200 and thats what he did. Go get a price quote from one
supplier and then take it to another for a competitive price match (usually
they will try to out do each other by $100 or so).

I wouldn't trust a crate motor. I've heard too many sad stories about
engines from Checker, Autozone, and the like. I have always rebuilt my
engines. I would rather get an engine from a junk yard and rebuild it.
It's not much harder than swapping engines, and you'll know what's in it
(pistons, rings, bearings, etc). Let a machine shop bore it to fit the
pistons, and balance the bottom end. They do hundreds of engines and
have the people and tools to do a far better job than you or I ever
could in our garage. The best part for me is putting it all back
together. Nothing will put a smile on your face like hearing an engine
you rebuilt come to life for the first time.

I recently rebuilt a '92 Mitsubishi 2.0L Turbo (4G63 6-bolt) for my '94
Eclipse (the 6-bolt engines have larger crank and rod bearings). I
started it for the first time on May 5th of this year, and it now has
just a little over 6,000 miles on it. During the rebuild I had oversized
stainless steel valves installed, the head ported, along with higher
compression ration pistons. I then installed HKS high lift cams, a
Walbro high output fuel pump, larger Denso injectors, and reprogrammed
the ECU. It will rip the tires loose in 1st when it hits 4000 RPM, and
will get me over 30 MPG if I drive it half way reasonable. Do I sound
like a proud father or what?