A standard 13b rotary is as heavy as a ca18de or L18 all without ancillaries.
Rotaries are compact hence their popularity in conversions.
With all ancillaries the twin turbo 13b is only 30 or so kg lighter than a fully dressed Gen 3 v8. An alloy alloy race 13b is just sub 100kg fully dressed. (racing beat - read expensive)
Yet still cheaper per hp than same weight race engines producing same NA hp.
Rotaries are thirsty, noisy and hard to find realible second hand ones as they
are usually abused beyond redline and rebuilt with re-used seals as a dodgy cost cutting measures by many backyard and by so labeled professional builders who know they will last 5km or a little more guaranteeing money in their pockets.

Id say the ca18 over the 13b
However id prefer an L series with Ka12e head or good L 8v head and turbo
over the complexity of a hydraulic 16v head.
L series engines are legendary for more than one reason and remove the need
for pollution gear.

just out of curiousity - is the car heavier with a ca18det or a 13bt? and secondly, is it possible to backspace the rotary further than the ca18det (or vice versa)?

I can never seem to get a straight answer as to the weight of a rotary engine. I'm also curious, due to the way the capacity increases - I suspect that the larger capacity rotary engines aren't that much heavier than the smaller ones, but could be wrong of course.

the rotor can make more power, but be prepared to spend a #OOPS#load of money. CA=better value for money.

I have had both a 13B Jport 1200 ute and a ca18det 1200 coupe
The Ca18det was better in every way: power,realiability,economy,legality instalatiopn and not to menchin noise and police atraction. Yes you can get more power from a 13b turbo but in my opinion pretty $$$ for a decent engine build box engine managment ect. I would stick with the nissan 4 banger if I where you.

i'd rather go for a factory engine.. maybe a well done setup A15 with wiseco pistons. or ca18det

hate to say it but power = rotor
just keep screwing the boost into it

Bob there is a fella down hobart that as done the rotary conversion in a coupe It is a 13b I think. He is going to drag it.I bought the back end off him he had a r31 backend under it when I sore it .He is a mechanic and it is a really good job I may still have is number some were if you wanted to give him a call.

I'd probably go the rotary, specifically because of the weight (or relative lack of weight) of the vehicle. The rotaries (and please bear in mind this is a relative thing) in general produce more power but less torque than a comparable piston engine, which should suit a lighter car and a race-car at that. Plus, there's something quite enjoyable about the powerband of a rotary, even a turbo rotary.

If you are talking relatively standard engines, and making a complete guess as to how many hours you might cover in a year of competition, it's hard to knock the reliability of either one I suspect - you'd be running for a good few seasons before even having to think about any engine freshening up.

I think to answer both sides of your question bob, it's a bit of a toss up, the rotary can be made to put out more power in reasonably standard trim and might be easier to fit to the car, but I dont think it will be as reliable as the CA in the long run.
my 2c

i'd go 13bt definitely for a track car, the drama's would be the brake master hitting on the intake and the clutch fork for the 13bt 5 speed other than that i had alot better time installing my 12a compared to the ca18det