I could write an Epistle on this question...
First we are comparing the 350 Chevy to the Ford 351W (Windsor)....not the 351 Cleveland.
The short version is that beginning with the 265...the small block Chevy has been in continuous production since 1955 with the 350 introduced in 1967 vs. the small block 221 Ford in 1962 and the 351 Ford which was introduced in 1969. Although many consider the 351W to be a member of the 221/260/289/302 small block Ford family...it is actually a new heavily upgraded design with taller block, bigger main journals and different firing order.
One reason that the small block Chevy has ruled as THE high performance engine for so long is that GM made continuous improvements to the same basic design where MANY new parts would interchange with older blocks. Ford, by contrast, would introduce a new engine series every few years often with limited or no interchangeability. Chevy seemed to be very conscious about insuring back-wards interchangeability. Ford did not. If they felt a new design was better... they introduced it... regardless if it created interchangeability issues. Sometimes the new designs were better. Sometimes they were not. But it resulted in a much larger inventory of parts that was needed to cover all the variations over the years. BY contrast a much smaller inventory of parts could cover many years of Chevy production. This appealed to the cost control efforts of aftermarket manufactures and usually when a new part was produced by an aftermarket company the small block Chevy applications would be the first to hit the market. Ford applications would come much later...if at all. This dramatically affected the ability of Ford builders to be competitive with Chevy builders at the track.
As aftermarket manufactures came on the scene it was a no brainer as to what products they should stock and could sell as a fairly limited inventory could cover a vast number of small block Chevy applications. Not so with Ford until later years when the small block Ford became so popular with Mustang owners. Today that gap is closing as Ford has made tremendous strides in matching small block Chevy popularity.
However, there are some basic characteristics of the Ford that are less or more desirable than the small block Chevy.
Chevy has five cylinder bolt/studs around each cylinder. The Ford 351 has four. This results in better cylinder head gasket compression on the Chevy allowing fewer blown head gasket problems all else being the same.
The 351W Ford is notorious for intake gasket leaks into coolant passages near the intake ports. Chevy intakes do not have this same level of gasket failure.
In Ford's defense they use a better quality cast iron in their blocks. It tends to be harder and wears better. The early 351 blocks in particular are some of the best Ford has made. GM used a softer grade of cast iron in their production small block Chevy blocks and only used higher quality cast iron in the Chevy racing blocks. (Note that the higher quality cast iron was also used in Buick, Pontiac and Cadillac production blocks...but not Chevy.)
Ford 351 Blocks also tend to have thicker cylinder walls and better block rigidity at a penalty of increased weight. For many years Ford had better quality, cleaner castings than Chevy.
Ford also tends to use better nodular iron crankshafts than the cast Chevy cranks. The cast Ford cranks are very durable and wear resistant. However Chevy used forged cranks in many high performance production applications. Ford generally stuck with high quality cast cranks instead.
One of the primary reasons Chevy had an edge was that the small block cylinder heads have always flowed very well in stock or nearly stock form. By contrast the Ford 351 head had an exhaust restriction that did not allow them to flow as well as a comparable Chey head. However, in recent years Ford and other aftermarket companies have offered heads easily the equal and often superior to the best small block Chevy heads.
Bottom line...if I had to choose one... it would be a small block Chevy. The selection of aftermarket racing parts is still greater than Ford and any shortcoming the Chevy might have can be overcome with an aftermarket part. The public domain of engine developement information on the small block Chevy remains greater. The five stud cylinder design is superior. Parts cost is less than Ford. There is no V8 engine you can build or rebuild cheaper than a 350 small block Chevy. Ford is close on the 302....but a 351 will generally cost you more to build than a 350.
Both are excellent engines....and I own both...and I own more 351W powered vehicles than any other. However if I were selecting between the two to build a cost effective, most reliable, best performing racing or high performance street engine it would be the Chevy. Just NOT in a Cobra.
But as far as buying a NEW car or truck...It will be a Ford. I will not support any vehicle brand built by a government controlled car company.
The nice thing about building a 350 "Chevy"...is that you could do so using nothing but aftermarket parts. Not a single item from GM...
Just my $.02....
Kerry
I do notice, however, that most speed shops stock Chevy parts. What's the reason? Just law of averages that there are more chevy hot rodders and more parts are needed by them? Do Chevy's break a lot? I guess my real question is, if you had a million dollar bet on the table to win a race and you were given the choice of a 350 Chevy or a 351 Ford, which would you choose and why? One race, one million dollars and unlimited engine build budget. We'll say it's a perfect world where the cars weigh the same, the track grip is perfect, you cut a perfect light, everything, perfect. Which is it?
Love your thoughts MikeyW. I bought my Cobra with a Ford in it cause I didn't want a chevy in a Ford & for resale reasons if I ever decide to sell. I will tell you this I LOVE my 351W. It roars & goes faster than any chevy I've ever owned. 
Mike, I have noticed the Chevy powered Cobra's seem to stay out there longer. Growing up, Dad always bought Fords, don't really know why (he owns a Chevy now). My first car was a Ford, however, I've had great Chevy's, Dodge, Saturn, and Mazda vehicles. All have had issues with fitment and squeaky/rattling plastic parts inside the vehicle. I really think the plastic parts use is out of hand, but I'm sure it's due to cost. Remember cars with metal padded dashes? Don't remember hearing those rattle much.
