The differences between these two logs sets is very technical. But to boil it down, Vented type logs can only be used in fireplaces with a working chimney that meet current codes. The damper is locked open upon installation must be kept open when burning. Placement of the logs can be changed to make the fire look different. The flame has a more orange look and soot is more prevalent in the chimney.
Water can rust the burner, grate and also damage the logs in a short amount of time.
Non vented logs can be used in firebox with no chimney but still meet current building codes. Once logs are set up and must stay in this configuration through out there usage. The flame is more blue with yellow tips and these logs produce no soot. In some cases they don't look that great in the fireplace. However, most of the newer models have come a long ways in the looks dept.