iphone ios running in separate thread

What is the best way to run code on a separate thread? Is it:

[NSThread detachNewThreadSelector: @selector(doStuff) toTarget:self withObject:NULL];

Or:

    NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self
                                                                        selector:@selector(doStuff:)
                                                                          object:nil;
[queue addOperation:operation];
[operation release];
[queue release];

I've been doing the second way but the Wesley Cookbook I've been reading uses the first.