The best (first) plan that Pang Tong suggested to Liu Bei should be defined as worst (third) plan. At that plan, Pang Tong suggested Liu Bei attack Cheng Dou right away with lightning speed. According to him, if Liu Bei attacked like a wind, Liu Zhang will probably did not prepare very well, this will led to the victory. The truth is, when Liu Bei chose the second plan, he moved his troops from Jia Meng Guan (葭萌關) and victory along the way until he reached Luo Cheng (雒城). There, he lost Pang Tong and used almost a year to break it down. So, if he has chosen the first plan, what will happen? Yang Huai and Gao Pei (Liu Zhang's officers who has been ordered to follow Liu Bei as 'guard') will attacked him from behind, he will faced two side wars. Plus, the people of Yi Zhou didn't really welcome Liu Bei at that time, if they did, Liu Bei should not need one year time to conquer Luo Cheng.
To be truth, i am doubt that Pang Tong good at military strategy. When Liu Bei first entered Yi Zhou and met Liu Zhang at Fu Cheng (涪城), Pang Tong advise Liu Bei to capture Liu Zhang. With this, he said Liu Bei can take the whole Yi Zhou without causing much losses. IMO, it was a risky strategy. When Liu Zhang met Liu Bei, he brought along 30,000 troops, they were loyal to Liu Zhang, there should be a fought if this really happen. Then, Pang Tong never considered the reaction of the people at Yi Zhou. Although Liu Zhang not a great lord, still he governed Yi Zhou for quite long, how will the people betrayed him in split second? If Liu Bei did take this action, he will be facing hard time at Yi Zhou. Luckily, he was wise enough to reject Pang Tong's offer.
