Dynamic Disks are an easy way to expand an existing drive's size but they have some inherent overhead and create a less fault tolerant environment. I would avoid them whenever possible for hosting SQL Server database files. I would go with multiple 250GB presented drives, each of which should be on redundant storage, and multiple database files. You can always add more drives and ndf files later if the data grows.

If your log needs more than 250GB initially or will need to grow beyond 250GB SQL Server supports multiple log files. SQL Server will only write to one log file at a time but it will start writing to the next ldf on another disk as needed whenever the active portion of the log reaches the end of the current ldf.

If the log file explanation was unclear let me know, hopefully it came across cleanly. Bottom line is multiple 250GB disks will do what you need and likely perform better and be more fault tolerant than a single spanned volume with multiple 250GB drives behind it.