You probably mean Reactome. Which one to use depends on what you're after or your preferences. All pathway databases (KEGG and Reactome are not the only ones) have their own approach and focus. Here are some differences I can think of between KEGG and Reactome:

• The coverage in genes and processes is different with KEGG being historically more focused on metabolic pathways.
• The granularity of a pathway/process can be different between the two.
• Reactome tracks the curation process, i.e. there are references associated with edges of the pathway graph whereas KEGG doesn't as far as I know. Also whereas the curation process in Reactome is transparent, it is completely opaque in KEGG.
• Reactome keeps track of protein interactions and complexes (if KEGG does it, it's well hidden)
• KEGG pathways are part of the KEGG ecosystem of resources which could be a strength if only how to link data across the different parts of KEGG was better documented.