Tunbridge Wells gets half the trains that Tonbridge does as the line splits and the other half go on to Ashford so commuting is much easier from Tonbridge (you can also go straight through to Victoria on the Redhill line when things are messed up. T/W you would need to change.
Tonbridge high street has seen better days but there is a good sainsburys, biggest monsoon in the area, lovely butchers, good independent bookshop and coffee shops galore as well as a decent sized waitrose. Everything else is either north farm (nr Pembury half way between T and T/W or Tunbridge Wells or Sevenoaks or Bluewater.
Transport wise the traffic heading north from T/W is horrendous you are competing with the school buses coming up to the grammars. Its just as bad heading south as you are competing with the buses for the 2 church schools and T/W boys grammar. What can be less than a 10 minute journey in the evening can take 45 mins most days
Housing is cheaper in Tonbridge - look at the surrounding villages, Leigh is lovely but on the cross line, Bidborough, Penshurst both lovely too as is Weald (That may come under Sevenoaks for secondary catchment, Penshurst and Bidborough come under T/W catchment for secondaries) There is a lot of good stock within walking distance of the station and the top of the high street around the Hilden prep schools is still doable on foot.
We have the Medway, the castle and a river festival with dragonboat racing, a huge park, swimming pool and lots going on for children.
I'm rather biased as you can tell.