Voted for tilemaps. I decided on using Game Maker for my current project because of this reason. The wizard for extracting tiles is perfect in game maker, but the tilemapping is moderate. C2 could make a stride in this area by doing much more, with copy past tile region, line and paint bucket tool, along with the tile wizard. 8)
As for the multiplayer, if your not going to implement it in an easy use form for non programmers, then why implement it at all if your not confident in programming it yourself? It's game maker tool, not C++. The idea is to make it easy for all users.