If the old and new cranksets have the same number of bolts to attach the chainrings and they both use chainrings with the same BCD (bolt circle diameter) then you will be able to swap gears between the old and new cranksets. Shorter cranks will require higher pedal effort to achieve the same forward thrust but the lower gearing of the new crankset will compensate or perhaps overcompensate for that. So your new and old cranksets may come out about even as far as the perceived effort for climbing hills is concerned although you will need to pedal at higher rpms for any given speed with the new gears which is ok if you like to spin. If the chainring mounting specs mentioned above match between the new and old cranksets then you could use your old gears if you find the new ones aren't quite what you want. If they don't match then either of the new options should work but the 44T option will get you closer to the same top gear you had before which is important if you find yourself riding near the top gear on your trainer (or in real life but you say not so much in real life).