As a Porsche nut, a very difficult decision for me... I could argue a case for any era, depending on the circumstances
I've never driven a 'performance' early car, but would love to try a 73RS. I'm sure the 3.0 would be faster, but the front bumper and rear wing don't look right to me.
I drove a 964RS around 10 years ago on the road. Didn't like it. Lovely engine noise, but felt way too stiff for British roads - might be nicer on a track. The 3.8 964 is supposed to be a wondrous thing... it looks mean as **** (but not in white), is super light weight, and has a proper engine.. I'd take one of those over any other 964.
I've driven a 993RS at Oulton Park... at the time (20 years ago), it was magnificent. But I don't think the 993 really moved the game on from the 964 that much. Plus I never really understood why people like the styling of 993's, and the splitter on the RS CS is hideous.
Not driven a 996RS, but have driven a MK2 GT3, and I read/heard they are a more extreme (ie; stiffer) version of those. Amazing engine/steering. Bit tricky on the limit. Very set-up sensitive.
No RS experience in 997's, but plenty of experience in GT3's, and these really are sublime! The gen1 RS isn't really much different to the GT3... the gen2 GT3 is a better car than the gen1 RS, and the gen2 RS is on another level. I would love a blue and gold 3.8RS
Now have a couple of hundred miles in a 991 GT3. After the initial 'WOW, THIS THING IS AMAZING' wore off, I don't think one would be for me, other than as a track day car. Yes, they are technically amazing, and you could easily run one as a daily (they are incredibly refined), but the gearing is way too long, and as effective as the gear box is, I'd prefer a manual.
Leaving the best (IMO) to last... the 4.0. For me, after a CGT, this is the pinnacle. Not massively different to the 3.8, but different in the right areas, Pretty much a full motorsport engine and a manual box. Involving (ie; challenging!) handling. All 997's have brilliant steering - better than the 991's.
So a 997GT3RS 4.0... preferably RHD, in PTS Mexico Blue like the one JZM have sold a couple of times... the last time for >£400k. If not, a 3.8 in blue and gold.
I would be very happy
EDIT....
JZM have a blue 3.8... where can I find £185k double quick?