Both series are excellent. The styles are very different from modern shows. Acting much more raw and unpolished, of course a bit cheesy at times due to 50 years of differentiating standards. But that's why i like it. There is no questioning the underlying subjects in both series, they carry the seriousness very well, with understandings between major ranking military personell, most of the time balancing on a knive's edge. It is no children's show, but children could watch it too, because there is little violence - another trait i find positive. A series that can convey seriousness and quality without excessive use of violence, is hard to do, and both of these series does it very well. Secret army is a few levels higher than Colditz, so if you select one, select that one. Even just watching the first season is good enough on it's own, the actor Christopher Neame portraying the pilot and spy John Curtis, carries it very well on his own, but of course all the other actors does great jobs too.



https://en.wikipedia.org/wiki/Secret_Army_(TV_series)

"Secret Army is a British television drama made by the BBC and the Belgian national broadcaster BRT (now VRT) created by Gerard Glaister. It tells the story of a fictional Belgian resistance movement in German-occupied Belgium during the Second World War, an escape line dedicated to returning Allied airmen, usually shot down by the Luftwaffe, to Great Britain. It was made in the UK and Belgium and three series were broadcast on BBC1 between 7 September 1977 and 15 December 1979."



https://en.wikipedia.org/wiki/Colditz_(1972_TV_series)

"Colditz is a British television drama series co-produced by the BBC and Universal Studios and screened between 1972 and 1974.

The series deals with Allied prisoners of war imprisoned at the supposedly escape-proof Colditz Castle when designated Oflag IV-C during World War II, and their many attempts to escape captivity, as well as the relationships formed between the various nationalities and their German captors.

Colditz was created by Brian Degas working with the producer Gerard Glaister, who went on to devise another successful BBC series dealing with the Second World War, Secret Army. Technical consultant for the series was Major Pat Reid, the real British Escape Officer at Colditz. One of the locations used in filming was Stirling Castle."