Although I can't comment on Scoobies I can give you some views on two Evos I have experienced.
Going back 4 years I had an Evo 4RS, it was std apart from a full turbo back HKS exhaust, decat, HKS Racing suction kit and grooved GSR spec brakes and Red Stuff pads. After 2 lightly modded R32 Skyline GTR's and a few other cars in between I now have an Evo 2 RS with rock hard suspension, half cage and Bucket seat, its std enginewise running std boost and std inlet/exhaust.
Due to the mods the cars are quite different. The 4 was quicker (RR'd at 297 bhp fwhp) and definetly handled better as an everyday car. I say this because the roads I commute on are terrible, I dunno what Aberdeen council spend the road budget on up here, its certainly not the roads, anyway, I digress, the car inspired alot of confidence and I was alot comfier in the 4. It was more refined than the 2 but you'd expect that given the constant development and model change between the 2 cars. I love the 2 for what it is, a cheap, quick and reasonably practical car. Once I get some more user friendly springs fitted and I get the HKS exhaust and Gizzmo chip on the car they should be easier to compare performance and handling wise. The 2 is quick and handles like a go-kart, it zips quickly up the revs but feels strangled after 5000 rpm. The chip and pipe should sort this out though.
Interior wise, the 4 takes it, it was better quality and after I fitted GSR recaros just about perfect, basic, functional and made it easy to drive very quickly. It was newer though, 4 years old when I had the car versus the 11 year old interior in the 2 which is a bit beat up now, I like it though, it has character and for a Back Road blaster it fits the bill perfectly, or it will with a few 60mm gauges
Given I paid 12k for my 4 back in 2001 it was alot more to lay out on a car than the amount i paid for the 2 earlier this year. If your budget will stretch to it, get a 4. The cars are comparible in the early stages of tuning, parts availablility seems good for the early cars, probably not as good as the later models right enough.
I guess you could pick up a 4 from about £8k, versus just over half of that for a 2, slightly more for a 3.
It depends on your budget though, I always allow plenty for servicing and mods because I know what the cars cost, don't stretch yourself too far and scrimp when looking after these cars.
Although I've never had an Impreza, I'm sure that they are good cars, if I did buy one though it would be an STi, a sharper car by all accounts and probably more comparible to an Evo, especially the later models, As far as I can tell, the Evo seems a harder edged car than the Impreza, chosen by myself as I thought it was more a drivers car. I'm not into this whole mine is better than yours thing though, its stupid, I like what I like and everybody else is entitled to their own opinion. I'd certainly like to experience a nice scooby, just to see what all the fuss is about.
hope i haven't bored you too much.....