LoBelly, that tyre smoke really compliments your RMC body shape well.
In my opinion there is no perfect Cobra, they all have pros & cons. I'm no expert, but here is my take. I'm probably the only one here stupid enough to try and write honestly about each car make.
DRB
Very early(pre 1995) had smaller rear guards etc and was based off Torana setup(live axle), then had what you would call 427 shape, still Torana, then body was lifted on the chassis I think 10mm to help fit EFI 302w engines(still Torana), then front guards etc got a little larger and a few other tweaks like dropped floor became standard and now offered in Torana or Jag, also modern dash available. All versions are monocoque(body bonded to chassis at the factory). Most have 302w, 351w is rare, new versions accomodate all modern engine choices.
Pros - very good performance out of the box, especially the later Torana based ones that everyone was fitting with Ford 9" rear. With a few tweaks it's very easy to have a competitive track car at the Nationals and also a great street car. Haven't seen much of the Jag based ones on the track. Have smaller wheel arches, so look like they sit lower than other Cobras, especially before the body lift. Have longer footwells. Doors roll over further at the top helping seal out water and make a nice arm rest. Nice deep dish wheels out of the box on Torana based cars.
Cons - one of the less original shapes, longer footwells means you can't have real side pipes and lots of the earlier DRBs have raised rear floors, so taller drivers can sit quite high in them(but helps in getting the mufflers/cats up high).
RMC
Only had 2 body shapes. I liked the first body shape the best, don't know why they changed. Body is separate to chassis. Runs Jag XJ6 series2/3 front suspension with generally shortened XJ6 independent rear. Most common engines are 302w & 351w, some big blocks.
Pros - a more original shape, can have live side pipes, nice deep dish wheels(although knock-off wheels still sit too far out in the guards in my opinion).
Cons - one of the heaviest I think, so not the greatest base for a track car, but a fantastic street car. Older versions are not so great on the road, need a few tweaks which are now done in the factory, also well known failure point in upper control arm mounting, which needs to be strengthened...this has also been fixed in the factory.
Classic Revival
Had 2 body shapes that I know of. Taller body. Body is separate to the chassis. All vehicles run AU independent Falcon rear-end and Jag XJ6 Series2/3 front-end.
Pros - taller body so easier to fit modern engines in, can have live side pipes.
Cons - no wheel dish at all, most seem to be set up for Holden/Chev engines, earlier CR's used Holden 5lt, later LS1, LS2, L76 etc. Too many forum members own Classic Revivals.
Robnell
Only the one body shape I think, ADR approved in it's day. Marketed as the premium Cobra in Aus and with a price to reflect this. Had a layer of Kevlar in it's body. Not many sold, no longer being manufactured. Separate body & chassis. Lots of big block versions around. Earlier ones were all small block I think.
Pros - well it's a Robnell, it's got it all - very nice body shape, live side pipes, great offsets for deep dish wheels, knock-offs look great, optioned with 6 pin knock-off hubs that were ADR approved.
Cons - a little flat in the front and
oil cooler hole spoils a near perfect body. Price tag.
Harrison
Only the one body shape, very similar to RMC but with rear guard lips etc. Offered in 3 lengths - standard, 50mm & 100mm stretch. Very flexible basis for a Cobra as you can choose virtually any engine & gearbox combination. Manufacturer also offers 4 rear-end choices. Earlier cars had fully fabricated upper & lower A arm front suspension, later cars have fabricated upper A arm and lower arms with control rods. Most cars use Skyline R32 independent rear due to the bang for buck factor, but will also see Ford 9" & Commodore live axle versions. Now offer fabricated independent rear with offset to suit deep dish/knock-off wheels. Very light Cobra, even features aluminium floors etc. Monocoque body/chassis unit.
Pros - Nice body shape, live side pipes, one of the lightest around so makes a great track car, also very well sorted road car. Wide choice of engines, gearboxes and diffs. Factory power steering an option. Built-in structural roll-bar support tubes. You name it, it's got it.
Cons - Skyline rear doesn't have a great dish, but better than CR. Not enough Harrison owners on the forums.
Can't help with any of the others as my knowledge is limited.
As a general rule, if it's an old car e.g. old RMC, old DRB etc, on average the build quality won't be up to par with later vehicles. In the old days, build quality was rough and cheap, not what it is today. It's also quite difficult/expensive to get these old dogs up to scratch.
I've owned three of the above kit brands.
I guess the 3 largest Cobra manufacturers in Aus currently would be DRB, Harrison & Classic Revival. This is going on number of units manufactured over the past 12 months. DRB has manufactured the most Cobras in Aus.
This is just my opinion, you will find that people will love the Cobra they have and with good reason, it's theirs. So no offence intended fellers. And to be honest cars are pretty well sorted these days and a lot comes down to build quality.