http://www.yaaastark.de/pentax/Pentax_DA70_FA77.htm
(in German, English Translated Page Here)
Whilst you can inspect and find out all the differences, pros and cons (comparatively), I think if I had to choose one amongst them, the decision is easy, that is, the focal length is just the determinative factor to me here..
A 70mm lens on a Pentax APS-C DSLR is 70 x 1.53 which is equal to 107mm. On the other hand, a 77mm lens is equivalent to an 118mm lens in 135 film sense, which is just too long to my taste for a portrait lens. In fact, 85mm to 105mm used to be my favourite range in doing portrait (of course in film sense). It is therefore the DA 70 pancake still fulfil my requirement, somehow marginally!