(just playing devil's advocate here)
to throw out another angle.... what are you going to do with him in the front seat that's different from what you would do with him while he's in the back seat? you can talk to him in either position. yes, you can reach him in the front seat, but if you are paying more attention to him than to the road, that could be an issue as well.
fwiw... luke has been known to stay awake until 10pm
with just a short mini-catnap. he's not going anywhere near the front seat.
good luck with your decision!!