MakerBot PLA Filament is the best and most consistent filament for the MakerBot Replicator 5th Generation, Replicator Z18, Makerbot Replicator 2 and earlier models.
MakerBot PLA Filament is a bioplastic derived from corn and guaranteed not to have any heavy metals, phthalates or BPA.
Note 1kg reels do not fit the following, but a customized spool holder might save you money:
MakerBot Replicator Mini
MakerBot Replicator 5th Generation
MakerBot Mini + - download spool holder and customize to use
MakerBot Replicator+ download spool holder and customize to use
However a printable spool holder is available on Thingiverse: Thing 721796 which enables the 1kg spools to be used directly with the MakerBot Replicator Mini 5th Generation and the MakerBot Z18 and customized for the MakerBot Mini+ and MakerBot Replicator+