Marin have always had a good reputation for quality. If you can't decide between a hybrid and a drop bar then I'd say that a cyclocross bike is the best choice - performance hybrids tend to have the limitations of each type. Eg they have narrow tyres that don't like trails or bad roads, but still don't have the advantages of a drop bar (more hand positions and better aerodynamics, so better speed.) But crossers have the advantages of each - you can fit wide or narrow tyres, and they have the aerodynamics of a real road bike. This makes a big difference when riding into the wind.

But, with your medical problems, the type of bike you go for isn't as important as the fit and fine adjustments that need to be made. Find a good store that offers proper fittings and read "Pruitt's Complete Medical Guide for Cyclists."