That's a tough question.
The RV-8 is heavier with a bigger wing. I would say the stall speed and approach speed to landing is similar, although I fly final a bit faster in the 8 and use full flaps. I have 16 hours on the 8, so I'm no expert.
They fly similar except the rudder inputs are different to keep the ball centered in turns. No suprise there, the T-18 is short, the RV-8 is longer. Similarly the pitch reponse is slower in the 8.
The T-18 is snug, before I 'lost' 25 pounds, I had to squirm in. The RV-8 is roomy, I slide around on the seat to get centered before I land.
My T-18 has the original airfoil with 6"x3/8" stall strips. In a stall, the left wing drops. It's leading edge is thinner than the right wing, especially at the tip, where the right wing has a landing light. Also I'm sitting on the left side. The wing drop is less with one notch of flaps, more with full flaps, so I land it with the flaps in the first notch. I added 2 small "Hall" vortex generators ahead of the inboard ends of the ailerons to reduce the wing drop and improve the control after it. The stall recovery in a power off stall, if done with minimal input (lift wing, slightly lower nose) can leave you in a secondary stall, fully controlled and falling like a piano, about 2000 fpm. Add throttle and the wings hook right up and begin a strong climb. The airfoil on the RV-8 stalls different, less abrupt. I don't have enough experience to add detail.
Because the T-18 fuel tank is ahead of the CG, landing with low fuel means landing with aft CG, and can be pitch sensitive. If I'm tired after a long flight, it can get ugly. My T-18 tracks straight initially on landing, but as it slows thru about 45 MPH it is harder to keep on track (Left / Right) worst about 35 and better as it slows thru 25? I switched from the Maul tail wheel to the Trusty tail spring with Vince's flyboy wheel assembly. That change improved landings, but seems bouncy on roll out over rough grass. Could be the softer spring rate of the stinger spring compared to the heavier leaf spring?
The RV-8 tracks well on landing, and is easier than the T-18. I have not flown it near aft CG yet.
The T-18 has a short control stick that takes very little movement, The 8 has a taller stick that takes more movement. Both are fine. Both have sensitive brakes, that are used carefully but respond very well when called upon.
Your question is a good one that I cannot fully answer. I intend to keep the T-18 and continue to explore the differences and similarities. It will be flown regularly, as I'm changing the engine in the RV-8, I just can't get comfortable with my Mazda turbo rotary engine. I have an IVO-360 enigine from a Brantly B2B that I'm converting, and the 8 will be out of service for a few months.