How can I make my NSTextField NOT highlight its text when the application starts?

I am using IB, there's a property on NSTextField called Refuses First Responder. Ticking that will prevent the highlighting of the text field immediately after the window is presented. There's some more detailed info about Refuses First Responder in this question.

Your text field is selecting the text, due to the default implementation of becomeFirstResponder in NSTextField.

To prevent selection, subclass NSTextField, and override becomeFirstResponder to deselect any text:

- (BOOL) becomeFirstResponder
{
    BOOL responderStatus = [super becomeFirstResponder];

    NSRange selectionRange = [[self  currentEditor] selectedRange];
    [[self currentEditor] setSelectedRange:NSMakeRange(selectionRange.length,0)];

    return responderStatus;
}

The resulting behavior is that the field does not select the text when it gets the focus.

To make nothing the first responder, call makeFirstResponder:nil after your application finishes launching. I like to subclass NSObject to define doInitWithContentView:(NSView *)contentView, and call it from my NSApplicationDelegate. In the code below, _window is an IBOutlet:

- (void) applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application

    [_menuController doInitWithContentView:_window.contentView];
}

The reason your field is getting focus when the application starts is because the window automatically gives focus to the first control. It determines what is considered first, by scanning left to right, top down (it scans left to right first, since a text field placed at the top right will still get focused). One caveat is that if the window is restorable, and you terminate the application from within Xcode, then whatever field was last focused will retain the focus state from the last execution.