I'm travelling from Krakow to Warsaw in October. I have two options, the bus costs $5 and the train costs around $15. I'm ready to spend $10 more in case the route is scenic. But, is it scenic?
I travelled the opposite direction by train (fast train) recently and while I did spend part of the journey sleeping, I can say that I don't recall seeing anything spectacular outside the windows while I was awake. It's flat land and a you will see rural landscapes plus the odd look in someone's backyard every once in a while.
Personally I would make my choice also based on duration of the journey and comfort.
I'm Polish and that route is not scenic. But train ride should be faster. If its direct connection than it should take 2.5-3h. Which train ride exactly you were looking at? Koleje Mazowieckie?
If you would take a bus - then probably you should take Polski Bus which was mentioned here. It's kinda nice - it has WiFi and usually they'll give you small appetizer. Also Lux Express might be travelling in that direction. However, bus may take a little bit longer (depending on the traffic). Usually 5-6h.
BTW If you will be travelling in Poland you can use this site: e-podroznik.pl You can get the timetables and prices.
I am from Poland and i use to travel on this route. The best way to go from Krakow to Warsaw will be a high speed train called Express Intercity Premium. It goes up to 200 km/h (125 mph) - bus goes up to only 100 km/h (62.5 mph). Travelling between both cities by theese high speed trains will take only 2:15 h. You can exit the train on stations: Warszawa Zachodnia (Warsaw West) near office buildings, Warszawa Centralna (Warsaw Central) - it is underground station in city centre or Warszawa Wschodnia (Warsaw East) in Stara Praga (old Praga) historical district near e.g. Google Campus.
First, the train is going by clasical railway lines no. 8 and 64. This segment is very scenic, it goes through old villages with wooden houses. Then the train enters high speed line called Centralna Magistrala Kolejowa (Central Railway Trunk Line, no. 4) which ends in Grodzisk Mazowiecki town. This line can be a little bit boring, but it is very fast. Then, on the end of this line the train enters four-track railway line no. 1. It goes through tight urbanized terrain, on second track pair there is a lot of suburban trains station. This line goes to Warsaw centre - behind Warsaw West station it goes into Warsaw City Tunnel (Warszawski Tunel Średnicowy).
I have taken PolskiBus from Krakow to Warsaw. It was somewhere between 5 to 6 hours. I took that bus early in the morning and I think just in the beginning there were some scenic areas. After that mostly it was just plain fields nothing exciting but you will be passing few villages on your way to Warsaw. I was coming to Krakow from Zakopane which is I think 1 to 2 hours bus bus and that route is really scenic. So basically there would be no big difference between bus and train ride. For cheaper option preferably I would suggest a bus ride.