I always think with the Byzantine army they were at times so spread out that total numbers aren't that relevant - it's what you can concentrate at one point. For example in 550 they had 150,000 troops on paper but couldn't put more than 5,000 in Hispania because of rebellions in Africa, trouble with Persia and the Balkans and Italy!Since 1150 was before the Fourth Crusade in 1204, the first choice would be the Roman or "Byzantine" Army, since it was the best army in Europe Constantly from about 200 BC to AD 1204, except for relatively short intervals.
The Huns may have been the supreme military force in Europe in the reign of Attila from 434 to 453.
The First Bulgarian Empire from 681 to 1018 might sometimes have had a more powerful army than the "Byzantine" one.
The Frankish military under Charlemagne and Louis I from 768 to 840 might have been more powerful than the "Byzantine" military.
Tsar Simeon I of the First Bulgarian Empire may have had a better army than the "Byzantine" one during his reign from 893 to 927.
The Caliphate of Cordoba in Spain may have had the best army in Europe in about 950 to 1010, although the "Byzantine" army was also very powerful about that time.
The Almoravid army which invaded Spain to fight the Christians in 1086 and returned to annex the Muslim states and fight the Christians in 1090, might have been the most powerful army in Europe for some time.
And there may have been other armies inEruope more powerful than the Roman or "Byzantine" one from time to time. But the Roman or "Byzantine" army was usually the most powerful in Europe and as far as I know 1155 was not an exception.