My wife and I took the Recoleta and Palermo tour with Marcos today. Outstanding tour! Marcos has an extraordinary knowledge of Buenos Aires' history, and was adroit at mixing amusing anecdotes of the BA rich & famous with explanations of their historical significance. His English is perfect. When I asked how he has become such an excellent raconteur, Marcos said that he had taken a class in stand-up comedy to polish his speaking skills (!) Of course, the fact that he was a Psych student might have also helped ... :+>
Tour took just over 3.5 hours, and included a walk in the Rose Garden and a tour of the Recoleta Cemetery (a word of advice - there is more to see in the cemetery than just Evita's tomb). Bicycles are new and in excellent condition, with large comfortable seats. Single gear, so no need to be constantly switching gears. The run was generally flat, with the exception of one hill just before the cemetery, so not too painful for non-cyclists like me.
Fee was US$40 or 320 pesos.
We wholeheartedly recommend the tour, and Marcos as a guide.