A34 - M4 is the way to go - my head office is in Bristol so I know the trip well. I have tried the "road through the middle" whichj goes through Salisbury and Bath - pretty but mostly single carriageway.
Agreed in theory with TGC but if your coming from anywhere near Brighton then M23 M25 M3 M4 is quicker (albeit longer in miles)
Avoid the Salisbury/Warminster way (shorter in miles but longer in time) And i personally would avoid A27/M27 .... Shite roads!
Agree with above - go to uni in Bristol and A27, M27, M3, A34, M4, M32 (into Bristol) is DEFINITELY the way to go, at least from Worthing and surrounding areas.
Probably still better than M25, even from Brighton area?
After evening games at Withdean I still take the route above, and give the M23/25 the swerve. Once you are past roundabout-land (Chichester) there is little reason to go below 95 until you get to the middle of Bristol.