Taking the train can be cheaper, too. For instance, I live in Zone 3 and a monthly travelcard for Zones 1-3 to travel on all Underground, buses and trains would cost me over £100 per month. HOWEVER, I simply have a season ticket for the train ONLY between my local train station and its central London terminus (Victoria station, in this case) and it costs £75/month. Much cheaper!!
And trains are often times less crowded than the Tube, those this is extremely variable based on what train/Tube you're talking about.
I prefer the train anyday, since it's not as stuffy or hot as the Tube - even though it runs slightly less frequently, it's really not a huge deal. Often times trains can be FASTER than the Tube. For instance, from Clapham Common the Tube takes 18 minutes, but the train from Clapham High Street or Clapham Junction takes 8 minutes. If you live near Clapham Junction, it's one of the busiest stations in Britain, so there's trains into Waterloo or Victoria literally every minute - just as frequent as the Tube.