XI and EDI: Mapping Strategy

I need to get some opinions on mapping approaches in XI. We're doing EDI with XI 3.0 and the Seeburger Adapter.

We're making design decisions now and the question came up whether we should build one map per IDoc-Partner-X12 transaction or one map per X12-Idoc pair and build in logic to take care of partner specific requirements.

I'm wondering how other folk have dealt with the same design decision? Any pros or cons on either side? I'm wondering about development effort and ongoing maintenance, particularly in production. Any insights would be greatly appreciated. Thanx!