Neither. I do not think they were particularly intimidiating - - mere boy scouts when compared to the US Robo-Cops. Surely, they were instances of police beatings but at least they did not shoot people.
Nor do I think thatthe secret service was particularly menacing. IMHO, the bult of police force in "socialist" was concentrated in investigating economic crimes, such as embezzlement, tax evasion, black market activities etc. - and they were very professional in that respect - neither menacing nor pathetic - just plainly effective.
The menacing secret police was a part of slef-importance mythology inveneted by dissidents, often to impress women. An example, a friend of mine was apprehended while distributing undergound literature. At the police station, he refused to answer any questions, but the cop insisted that he cooperates so they both be over with it. To which my friend replied defiantly, "And if I do not, thenyou will beat me up"? The cop smiled and said "You want us to make you a martyr? No way." Th ecop just confiscated the leaflets and let my friend go. To my knowldged, most interrogation of dissidents ended ina similar fasion, although threats or offers of cooperation were sometimes made. The swecret service did not do the beatings - this was the domain of patrolmen in charge of policing to lower class behavior (public drinking, disturbing the peace, etc.). An those who usually got the beatings were usually working class people - I have never heard of cops treating intelligentsia with disrespect.
BTW. no you could recognize a plaincloath cop most of the time. There were counless rumors in dissident circle who was an 'agent' but that was a part of dissident mythology rather than empirical reality.
wojtek