Very definitely the rear wheel.
The front can come off in seconds, the rear cannot.
That's presuming you have a very strong chain and lock.
If your lock is a fairly standard one it makes no odds which wheel its on.
Four decades on two wheels has taught me nothing, all advice given is guaranteed to be wrong
yep. Its pretty chunky.. only downside is I would prefer an integrated chain lock rather than a padlock one which effectively is 3 bits. But you cant have it all!
Xena xx6 (alarm disc lock) coming tomorrow. Might use just that while its sitting in back garden in ear shot.