Can't comment too much - being a country bumpkin from the West and not really knowing either of the areas (had to google where Northolt was), but geographically & easy access to 'green' areas Fareham looks a far nicer place to be...!
Northolt well within the M25 and even if you head the shortest 'way out' you're straight into a very busy part of the country around Slough, Watford, Windsor and such. Will be around there shortly (stay in Bracknell before a day at Legoland Windsor) and can't imagine trying to ride around there as the roads are horribly busy and very little 'road cycling' space! The segregated cycleways around Bracknell (walked around a few times) look good for commuters, but just means there very little else on the roads themselves.
Very different world to me... Several points yesterday would ride 20-30 mins with only seeing a couple of cars.
Even 20 mins this 'busy' stretch of A road on a sunday afternoon probably only saw ~20 overtakes. Almost zero need for cycling infrastructure (none along that stretch, except a couple of bits of paint on the road in the town).