What are the main differences between the two? I'm willing to run only another EXE from my (C++) application. Are there any differences when inheriting environments, security features etc?
The main difference between CreateProcess and ShellExecute is the following: CreateProcess is more oriented on low level and ShellExec on the high user lever which see the user in explorer.
For example using of CreateProcess one can use command line which length is more as MAX_PATH. It has 32,768 characters restriction. You can also use CreateProcess to start program (if you have enough permissions) on another windows desktop like on the Logon Screen.
Another example. You can use ShellExecute to start Control Panel or open any program which existed on the computer for editing of JPG filed for example. So you works with ShellExecute close to the corresponding actions in the Windows Explorer.