In regular army manpower count (which does not necessarily equate to the "strongest military") in 1977, the Warsaw pact had these numbers:

USSR - 455k

Poland - 204k

Czechoslovkia - 135k

East Germany - 105k

Source: http://www.cbo.gov/sites/default/files/77doc579.pdf

In 1969, Defense expenditure by Warsaw Pact nations (in dollars ms) is given as:

USSR - 42,000

Poland - 2,000

East Germany - 1,900

Czechoslovakia - 1,600

Rumania - 600

Hungary - 500

Compared to NATO:

USA - 78,000

France - 5,600

Britain - 5,400

West Germany - 5,300

Canada - 1,700

Holland - 900

Belgium - 500

Denmark = 300

http://osaarchivum.org/files/holdings/300/8/3/text/112-3-112.shtml

By these two measures, Poland would seem to have had the strongest military in the Warsaw pact in about 1970, other than the USSR.

From what I remember the East German army was very well disciplined and trained however they were not very numerous. Poland had the second largest and most populous. This is also important because they were the most anti-soviet of the Warsaw pact countries despite the border they shared.

This book covers it quite well. A Cardboard Castle?: An Inside History of the Warsaw Pact, 1955-1991 By Vojtech Mastny, Malcolm Byrne