Scud v. 458: The 458 for sure, the Scud has a stupid name and I've never liked the way the F430 looks. I'm not a huge fan of the 458 but I wouldn't turn one down.
Sagaris v. Caymen: Caymen, I don't know much about TVR's but the little I do know I wouldn't want to own one. I also think the Caymen looks better, the Sagaris looks awkward.
Arnage v. XJ-8: The Bentley for sure. The only people who seem to drive Jags around her are eccentric rich women in their late 50's early 60's.
Wrangle v. Defender: The Defender, it's in the top 3 of my dream car list.
MGB GT v. Cooper S: The only people that I've ever seen drive MG's are nerdy men in their 40's who are either divorced or never married. Plus they don't really scream reliable. I've driven Cooper S's though and I rather like them so I'd go with it, not saying the reliability is any better though.
Skyline v. Supra: Not sure on this one, both cars have that aura that attracts nerdy pre-teens who fawn over them like they are some kind of holy Japanese relic. I'd probably go with the Supra because they can look halfway decent in white without the spoiler and a nice set of deep dish wheels.