Ed, I don't even know which plan makes more sense, but my attempt at reasoning it out goes as follows.

Harper's offer of a deisel tax reduction is typical of his solutions - it looks simple and fair at first glance, and looks as if it might help keep other consumer prices down. But experience tells me that at the retail end, the prices will not go down, and users of deisel equipment will not make any further effort to cut their costs by going to more energy efficient vehicles and equipment.

Dion thinks the tax money is better spent on infrastructure and spreading some of it around, and placating the direct users of deisel with incentives to go energy efficient and giving them a financial hand while they do it. Of course, the cost in there will be administrating where the money goes and vetting who gets it.

So I think maybe Harper's plan is not as happy as it looks at first glance, and I think Dion's plan will likely cost more money in the short run. OTOH, I have to wonder where Harper will find the income originally obtained from that tax to fund whatever it was already paying for.

Overall, I think Dion's plan, perhaps more expensive (or maybe not), is more responsible, and offers a better environmental outcome as well as short term alternate relief for deisel users. But it is more convoluted and difficult to explain to taxpayers (and deisel users).