I would give a slight edge to Richards. Seguin edges Richards on SOG and possibly PIM. Richard should out point Seguin this year. In a keeper I would go with Seguin but since this is a 1year go with Richards.
In a one-year pool, I think I prefer Brad Richards.
However, depending on roster allocation, Seguin might be able to be slotted in the RW - which can be a thin position in certain leagues.
I prefer Richards - if he offered it to you then tell him you will do the deal one for one (and that you don't like losing the RW eligibility but that you think its still fair).