My experience is with F1 (Canadian GP 2014, 2016 @ Circuit Gilles V), IMSA (Mobil1 GP and PWC @ Canadian Tire Motorsports Park "Mosport"), the Canadian Rally Championship (@ Bancroft) and NASCAR (Daytona 500 waaaay back when i was pretty young).
Ill go through some of my experiences which have been awesome so far.
Formula 1:
F1 was my first circuit racing experiences and something i think every race fan should go and see at least once. The cars are faster than anything ive ever seen and the events infield are incredible and are super immersive. F1 does everything BIG, not as big as NASCAR mind you, but for circuit racing, it was huge. There was so much to do, so much to see, we got there at 7am, got our seats (General Admission) and then went for walks the entire day up until the race and still didn't get to see everything. The opening races were fun (F1600, Ferrari Challenge Cup, Masters Historic Trophy) however there was so much to do infield wise that we missed most of the races. One of the nicest things about the circuit (may not apply to all F1 venues) was that even if the cars weren't at your corner, you could watch one of the massive jumbo screens so you didn't miss a thing (no need to re-watch). The race itself was mind blowing in 2014, as i had never seen anything that fast and i was just awestruck by the speed and technological efficiency of the cars. However, in 2016 i was less impressed as i had now been to many other races... Which leads me to the faults with going to an F1 event.
As i said before, everyone should go to at least 1 F1 event, however after that i don't know if i would go for a third time unless there are some big changes. First of all, its expensive, significantly compared to any other race i've gone to int he last 5 years. It cost $99+ CAN to do General Admission, and $250+ for a good grandstand, which is pretty pricey, especially considering i'm a student so my budget is around 0.40 cents, and that's just a single day pass. Pair that with the fact that the racing is pretty boring track-side... Not a lot of side by side battles, and if they are they are in areas that you need to pay $$$ to access (grandstands etc.). On top of that, most passes are done on long straights under DRS which is happening at such speeds you don't really get to see the action anyways... In my opinion, the spectacle of F1 is worth it the first time, but past that i find myself sitting and wondering why i'm paying $10 for watered down beer.
Mosport (GT/Prototype Racing)
By far my favorite, it is the best racing experience i have had, and it continues to be my "favorite weekend i've ever had" every year. To counter F1, the price is insane, $65 CAN gets you a full weekend pass (that's Thursday to Sunday!!!), includes pit walk, driver autograph session, paddock pass, and with the amount of money you'll save on beer (you can bring your own) you can buy a camping pass ($75 per car and trailer) and you can camp right next to the track. Mobil1 and PWC offer lots of opening races so you'll have something to watch all day, and the main events always offer super close wheel to wheel racing, lots of different manufacturers and models, and the racing is all out so you get to see photo-finishes, insane crashes, and awesome passes right in front of your face. Your pass also gets you access to ANYWHERE on the track, first come first serve basis so i just make my way to Moss Corner (5 a and b) in the early morning with a cooler full of food and beverages and i spend the day (race-day) watching all the action 10 feet from the edge of the track! Sometimes ill do the pit-walk and parade which can be very cool, but i usually get my "up-close" fix Friday and Saturday. On Friday and Saturday, I wake up, and spend my day near the events center and paddock. The events center is much smaller than F1, although the paddock makes up for it. The paddock walk costs and arm and a leg in F1, but is included in the Mosport tickets. You are able to go right into the garages (as much as they will let you), you can talk to drivers, engineers, team officials, as well as get up close and personal with the cars. I even had the opportunity to tag along with a group and got to sit in the Audi R8 LMS Ultra, before being promptly escorted out as it turns out it was for "friends and family only" oops... After races and sessions, the cars will be outside the garages for people to walk around to get a 360 view of the machinery, and if you get there early you can usually grab some "discarded" damaged pieces. The driver autograph session is also available, in which you get a large back of "swag", posters, all signed by the drivers. You also get to do a quick meet and greet with every driver. This is what makes GT/Prototype the most attractive for me to attend, and i highly recommend going to watch a race yourself!
NASCAR
I wasn't a huge racing fan when i went to this race so i don't really remember much (i was also very young). I have seen NASCAR at Mosport and its pretty cool, lots of bumping and grinding, just not my favorite series to watch. I do remember it being insane... So many people, and its produced better than any other racing series, just not my cup of tea.
Rally
The Canadian Rally Championship is very small and doesn't feature any top spec rally cars, however it was my first stage focused rally championship i attended and it was pretty cool to see. I was with a local so we went to some good spots to watch and i would definitely go again. The best part of Rally is the people, everyone is super nice and there is always a bush party breaking out somewhere! Issue is that you don't get to see "as much"...
I also saw the GRC is Ottawa this year and it was awesome, another first for me as i had never seen an RX race before. It was pretty cool, great bang for your buck ($40 for a ticket i think? got them as a gift) so it was well worth it. I heard there was a lot of activity surrounding the event too however i had to leave early due work so i didn't get to experience the entire show, hopefully next year

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In conclusion, go to whatever you can, these are some of my experiences but you should make your own! I thought for sure F1 would be the best, and id never change my mind. However after going to Mosport, i cant think of a better spectator experience (unless i had $10000 to spend on an F1 weekend). Basically, my advice is don't restrict your scope, go to everything you can, no matter what your past experiences or preferences are, because they are all fun, and they will all lead to a well spent weekend! If i missed anything just ask and if i remember more ill try and add it!