Tf2 automatically puts the video settings at what it thinks are the optimal settings for your computer. The ideal levels are marked with an asterisk.
In game, open up the console with ~ and type net_graph 1. This will make the game display your current framerate and see how well the game is performing at the current settings. Net_graph 0 will remove that info.
My suggestion, go for fps/performance over better graphicsif you arent getting 60 fps, sacrifice environment detail settings, etc...to let the game play more smoothly.