I'll try to answer your two questions first:
Can they be used in conjunction with one another to increase the amount of water retention in my soil?
As true Swales are always on contour (0deg slope) and Keyline plow rips (sub-soiling following the Keyline design method) only have one rip line on contour and the rest sloping towards the ridge I see them as not being possible to use together in their 'true' versions.
The Keyline plow rips are like mini swales with a slope toward the ridge, so if you wanted to replicate it while not having such a ripper you could potentially dig by hand and choose to make them as small 'swales', but these 'swales' are not then on contour (0-deg slope) so then not true swales but rather diversion ditches.
Once an area is well Keyline designed it will have the water retention and soak-in capacity to not have much run-off to talk of, but the Keyline design does include belts of trees (the same as a swale is intended to have trees, and other plants, planted in it and on the bank to maximize its water harvesting capacity).
Is one better than the other?
This answer is always 'It depends!'. What is your use of this pasture? Do you intend to ever run machinery over it, haying, slashing weeds etc.? If so, my guess is, the ridges and valleys of the swale(s) will be in your way, while the decompacted ripped soil will all be under ground so not in the way.
As I was hinting to above though, if you don't have a sub-soiler that can handle the curves that you will be following with the tractor, or of you plan to do the earth works by hand or with a digger/dozer you will need to choose swales.
I highly recommend you read 'Water for every farm' by PA Yeomans for a greater understanding of water's behaviour, and Keyline designing and its potental (even though it is not the easiest book to read).
Best of luck,
Esbjorn
