I would also rank 一野 the lowest simply because it did not participate in a decisive battlle.
二野 & 三野 - Battle of HuaiHai (hardest fought battle)
四野 - Battle of LiaoShen
四野 & 华北野战军 - Battle of PingQing, although Mao personally directed 华北野战军 before 四野 entered the Battle.
二野 & 三野 - Battle of HuaiHai (hardest fought battle)
四野 - Battle of LiaoShen
四野 & 华北野战军 - Battle of PingQing, although Mao personally directed 华北野战军 before 四野 entered the Battle.