Actually, I rarely recommend any specific choice. I think the key is to think hard about intended mission, then factor in the strengths and weaknesses of the various choices, and tailor to that mission.
Not much question, a RV-8 with a light nose is the more pleasant sport flyer. A heavy nose puts the CG against the forward limit when solo. Most run out of nose up trim when slowed for final, flaps fully extended. Maneuvers like a simple 3.5 G loop entry are better done two-handed, as the required stick force is high, which feeds a one-handed tendency to pull in a little right roll. A heavy metal prop boosts gyro forces, noticeable in rapid maneuvers or simply picking up the tail on takeoff, and it's hard on the crank at high pitch or yaw rates.
Downsides? Rear seat and baggage capability is reduced. An RV-8 loaded to the rear limit has very little pitch stability when slowed, and little stick force gradient with G increase. It's not difficult to fly, or unsafe for the aware, but it isn't pleasant.
Power: Angle valve 360's, 390's, and 400's with a constant speed pull like draft horses. Do a formation takeoff behind a parallel valve 360 fixed pitch, and you find yourself at partial throttle, wondering what is wrong with that guy's airplane. Build tip; an angle valve motor just barely fits in the standard RV-8 cowl.
Ahh, so pick a hot-rodded lightweight engine? Let's get real. It's not hard to get more power out of a Lycoming, but nobody installs upgraded parts. In addition, a pumped up parallel valve can be a challenge to cool; limited fin area, and you can't use the power if CHT is too high. I usually suggest against mods strictly for increased HP, and besides, most of the HP claims heard on the FBO porch are BS anyway. I'm not sayin' mods are bad. Things like porting for flow balance and electronic ignition make the engine a pleasure to use; any little power boost is gravy.
So, back to mission. If the airplane is going to spend most of it hours solo, mixing it up with the other local lunatics, giving rides with zero baggage, etc, I'd look at a composite constant speed and a parallel IO-360-M1B. Build it light, and you're talking Big Fun.
If the mission focus is cross country with wife and baggage, an angle valve with a metal Hartzell is the better hauler. In a pinch, either choice can do either mission.
My own is a 390 with a metal Hartzell. The mission was hauling Ms. Patti, complete with, ahhh, stuff, or a buddy and an heap of camping gear, or a few cases of Spotted Cow. The fastback increases rear baggage volume. I don't fly aggressive acro, and rarely G past 3, so the required stick force for pitch isn't a big deal. It can be hot where I live; the 390/CS combination bullets up to altitude quickly, at gross. Light, solo, cold air? No such thing as too much power, here made with displacement, not high cylinder pressure.
It fits my mission. Think about yours.