It's really a matter of whether you want to learn high-level, abstract concepts to games or whether you'd rather get down and dirty with a lot of the code basics that make up games.
I usually consider game development to be focused on the design and implementation of tools and platform solutions that aid designers in creating games. Game development isn't as much about creating the game as it is to creating the foundation that games can be built and managed. This is essentially your programmers.
Game design is on the receiving end of this foundation & tools. This group is often what drives requirements to the programmers and this is the group that takes those tools and creates an virtual world filled with interaction and fun packed adventure. These are often the creative types, ones who may have some minimal technical skills to write simple scripts in UnrealScript, Lua, Mono, etc. But these guys aren't the ones programming in C++ and concerned with engine code, network code, and how all the nodes of an MMO process hierarchy communicate in a distributed fashion.
Both have advantages & disadvantages to going into one or the other first, as with any choice in life. What drove me to development was the fact I enjoy programming, and so the choice was clear. If you're on the fense, then consider which avenue appeals to you more and start there.