Yeah, let me just quote something here. I think this is base on overall strength
1. Vietnam
Vietnam, like many other states in Indochina, had been underestimated many times. Vietnam has the fastest growing economy in Southeast Asia, though they're still relatively poor. Its army is the biggest in the world and if its reserved troops and paramilitary troops are counted, they have the second biggest army in the world. They also have the third biggest population in SEA. It has been involved in the 2 major wars against the 2 biggest major powers, defeated US, and a short later defeated China's invasion under a Chinese's fake reason of Kmer-China relation. More than 400 tanks of China force were destroyed and (around 250,000 both Chinese and Vietnamese troops dead) in that 1 month war. Chinese casualty claim: 6,900 killed, 15,000 wounded.[3] Western source: 26,000 killed, 37,000 wounded and 420 tanks destroyed.
2. Indonesia
Indonesia has the biggest population and land in the region. Their GDP is by far the highest in Southeast Asia. Indonesia is also the most powerful country in Southeast Asia politically. It is one of the founding members of ASEAN and APEC and they also have the third largest army in Southeast Asia after Vietnam and Burma. They're like the China of Southeast Asia.
3. Malaysia
Malaysia is one of the most technologically advanced nations in Southeast Asia. Just after Brunei and Singapore, they have the biggest GDP per capita. Though their army might not be the biggest or one of the biggest in SEA, it is certainly the second most technologically advanced after Singapore. They are also a founding member of APEC and ASEAN. Malaysia is sort of like the Japan of SEA.
4. Thailand
Thailand was the most visited country in SEA (before their political crisis). Their GDP is the second largest in SEA after Indonesia's. They also have the fourth largest army in SEA. Thailand is like the France of SEA.
5. The Philippines/Singapore
I had a hard time deciding which should be the fifth most powerful, so I'll say both are. The Philippines has the second biggest population and the third biggest GDP in SEA. The Philippines also has one of the biggest armies in SEA.
Singapore is the second richest country in SEA in terms of GDP per capita. It is SEA's main economic capital and despite the fact that they don't have natural resources, its economy is doing quite well. Singapore is also the most technologically advanced country in SEA.
lol. size of army is not representative of quality.
china has a freaking large army, but the US can easily match them with a smaller army.