Hmmm,,, should I post my opinion here and risk going down in flames?
What the heck, like water off a ducks back, here goes!
Assuming your physically fit and don't require an automatic trans, not overly big and don't require a 'larger than life' Cobra replica and am not afraid to spend 'enough' to get a reasonably accurate replica....
Select a model with an accurate 'look', that even applies to the 'larger than life' models out there. For instance a Classic Roadster is a little longer and wider than the vintage cars BUT it can be made to look more correct with the right exterior appointments. Like wheels, wooden steering wheel, dash and guages (laid out in a more correct manner), single roll bar, close to original style interior, etc. Even bolt on wheels can be had in something that at least approximates the vintage look. 15" tires help a TON in this regard (over all look of the car).
If it's an FIA style car, very nice choice, try to stay close to a period correct look for THAT car. A modern small block, even a crate motor, can be made to closely approximate the look of a 289. Not much point in going with a big block in an FIA style body. Going with the classic 427 S\C body style? Do yourself a favor, stay with a Ford big block. 390, 427, 428 etc. These motors all 'look' about the same.
Top dog selection might be considered a modern CSX car from SAI, but it's pricey and unless you REALLY appreciate having that CSX vin the authenticity would be lost on you. Kirkham is always a good call for that 'authentic' look. Hard to beat ERA for a good look AND great quality. An older used replica can be an excellent choice for a really authentic build at a decent price. Hi Tech (the OLDER ones in particular) are often excrutiatingly detailed to exacting vintage specs at a nice price. Contemporary, Unique are also worth a look.
Don't care 'that much' about an authentic look (shameful, but it seems to be more common than ever around here)? There are a number of 'also rans' at a good price.
Whats REALLY important are the fundamentals:
Wheels, interior, motor selection, body style, shifter (even a five speed can have a period correct looking shifter at least). I understand the newer FFR's have improved the look of the rear end, not sure about that, but clearly it's a car that needed help in this area. Budget will be a huge factor in your search, no matter WHICH one you select it's a virtual given you WILL exceed your budget. Even if you buy a used one, that rule will apply, as it will certainly need certain modifications to fit YOUR needs. Some say a Cobra is NEVER done, and I concur, there is always something that needs to be 'tweaked'. It's one of the things that make these cars fun.
All though not currently listed for sale, mine could be had for the right dollar amount. Take a look in my gallery by clicking the camera icon. Maybe YOU don't like the black out hood I have. Figure about 500 to 600 to have it painted to match the car. THATS the kind of things you usually end up doing to a used one. Changing this or that to YOUR specs (thats what happened to me)!