I believe doc is recommending the JW from experience

Its location is perhaps better for tourist activities, while the Renaissance might have the edge for nightlife, but both are in the same general area. The JW is higher up in the Marriott pecking order, but seems less consistent according to various FT posters.

The package including airport transfer is not as good a deal as it seems, as the best way between KLIA and downtown is now the new KL Ekspres train, which is faster and cheaper than road transportation.

As long as you get a room in the Renaissance Wing or at the JW, even the basic rooms are quite nice. Given the low occupancy rates in KL you should have a fair chance of getting an upgrade.