Chevrolet: late model sports cars, liter engines, valve seals

Question
im condsidering buying either a new mustang gt 4.6 liter/ or maybe a used 2002 camero or firebird 5.7 liter with low miles.  first in order which car is the fastest, second fastest, and third. and also which in your opinion would last the longest with limited problems motor wise.  ive been told that the mustamgs 4.6 liter engines manifold gasket lasts only about 60,000 miles or less cause the manifolds made of aluminum which gets alot hotter than cast iron. also told that the   valve seals go at around 120,000 or less. are either of those two true and if they are about how much would the dealer charge 2 fix this if its past my 3 yr 36k warranty. i havent heard anything about the firebird and camero engines. and do you know what gm certified used cars is length of coverage? i can only finance up 2 the high 20's and would like a sports car with speed, these are the only 3 that i would be interested in. please give me your expert opinion. i need 2 buy a car as soon as possible i aprreciate any advice you might offer thank you very much


Answer
I couldn't tell you which car is faster out of the 3, but the camaro and the firebird are the same cars. I know that we get alot of mustangs in on trade and in my opinion they are junk. They're ok for about the first 2 years and then they start falling apart. I had a camaro for about ten years that never gave me any problems. It had 260k miles when I got rid of it and it still ran strong.
Take your pick between the camaro and the firebird but stay away from the mustang.