Conventional wisdom when going to medellin is to go stay at the Mansion or the Castillo, hang out by the pool with the rest of the gringos and check out the chicks that drop by there. this isn't necessarily a bad plan. In fact, it''s generally a pretty good plan for a day or two, if only to collect a bunch of numbers, especially for unilingual English speakers. Having said that, this is also the most expensive way (value-wsie) to stay and monger in Medellin, particularly if you re travelling with friends. I also say this because there is a definite bullseye painted on the Mansion properties and there are enhanced risks of robberies (the hotel and guests have been assaulted and robbed on more than one occasion by masked robbers) so while I choose not to stay there I do admit to the girls and bros factor being a definite draw.
My recommendation would be to rent a private apartment. People make some good arguments for staying in various parts of town, but I do like to stay in the Parque Lleras area and grab a cab wherever. Everywhere in Columbia is chica friendly, basically, so I would rather spend my money living in a palace at hotel prices. I've rented awesome Penthouse apartments for less than what I'd pay to stay in a decent hotel, and as a party pad for the chicas they can't be beat. There are several services around, but I have been very pleased with the service and attentiveness of these guys, so I can recommend them. The website is You are not allowed to view links.
Look in the rental section and find a place that suits you. There are other reputable agencies around town that do this as well, so search around if you're open to the idea of quieter (maybe) private spaceLinkback: http://ifoundthechicas.com/colombia-hotel-and-apartment-rentals/172/first-american-realty-medellin/6517/