Previously, I have had centreline aeroplanes, Champs, Citabrias, Zlin 526F, Christen Eagle.
I am very comfortable with centreline, the communication is fine because the majority of communication is aural - the real experience is outside, looking at the wonderful scenery and experiencing the stunning performance.
However - we built a 7 first............
The reason was because of the likely flying my Brother and I had planned. Trips out, a bit of touring, some aerobatics - i.e. a good all round compromise.
The immediate access storage on a 7 is great, not so in an 8.
If you are of larger stature, the a 7 can be a bit of a squeeze, especially if you use the standard Vans belts
The 8 will give you and more so, the passenger plenty of room.
I remember my first Champ had the wide back seat - marvellous, I would put the passenger up front and lounge in a very relaxed manner in the back.
The final decision shouldn't be difficult, it is what you want the aeroplane to do for you when you are flying.
Resale - both will sell equally well - why would you want to sell an RV - unless the next one is ready ?
As Andy said - either will be great, provided that the steering wheel is where it was designed to be - at the back......