Forgot to mention about access to the lake through Mozambique. We traveled in Mozambique from Mulanje in Malawi across to Ilha de Mozambique in January 2011. We used public transport and had a great time but the infrastructure is poor and regular bus service is not available on all roads. Things may be easier if you have your own transport (not sure about road conditions) and if there are flights available but this will probably cost a pretty penny.
I know of one lodge on the Mozambique side -
Nkwichi Lodge ? Luxury Beach Lake Malawi. In 2007 we met someone traveling there and were told that most visitors come via Malawi.
I would opt for access from Malawi to see the lake.
Karin.