How much worse is this TLK train for crying out loud?
They're fine, though sometimes jammed at weekends in the summer or just before and after public holidays.
Or are the EIP trains just that much more amazing?
Certainly very good.
My question is, how likely is it that I will make the 19 15 train from Warszawa Central to Krakow with an arrival time of 17 50 at the airport?
If you have hand luggage only and everything else goes smoothly, no problem. If the plane's at a remote stand and they bus you to the gate, and if you're at the back of the plane so not on the first bus and have a queue at passport control due to other larger planes coming in at the same time plus (the real problem) to wait for a long time at the luggage carousel, then you're cutting it very fine and should get a taxi to be safe.
If the plane is delayed by a few minutes you will definitely need one to get that train luggage/queues or not. A taxi to Dworzec Centralny should only be about 40-50zl from a reputable firm.
jon357 says the buses are right by arrivals, so I should be able to get there quickly. Can you buy the ticket on the bus and is it more expensive if you do so?
Assuming you get to the arrivals hall with plenty of time to spare, walk out of the nearest door. You'll see first of all the taxis in the first lane, then several lanes with a zebra crossing. Look ahead and to your right a bit and you'll see the bus stop (I think on the third lane) about 30 seconds walk away. There will probably be a few people waiting. The ticket machine is next to the bus stop. You can buy from the driver also (though they do run out) and you will need coins for this.
It's a bit of a Catch 22 situation. You could be coming through the barrier at 1830, in which case you will definitely need a taxi and would need to have booked the train online unless you're lucky. If you're out early you'll have more breathing space though and I was outlining the worst case scenarios. A cab is still a good idea. You could get the later train or pay a bit more or a faster one and then get the bus at your leisure. If the difference in price between TLK and EIC isn't much more than 40-50zl this is probably your best bet.
I've winged it like that a few times and always (so far) been lucky however I've often had to get a taxi when I'd been planning on getting a bus.