Hi Summer. I definitely have seen an improvement on Levemir. The main benefit is that his curves tend to be much more predictable...i.e. actual "curves", with the AM and PMPS very nearly always higher than his nadir. (except yesterday, of course!) So that predictability has helped a great deal.
The Levemir is stronger in Fred, in that it can get him down to blue almost every day, except when he's really bouncing. With Lantus, he'd be all over the place. Conversely, because he's such a bouncer, he goes way down and way up each day, and that can be hard on him. But, his drinking and urine output has completely normalized, and they were both extensive right up to the switch. So though he has really ugly numbers..usually each day

....I may not be catching all the GOOD numbers that have helped him normalize in that department. He's also on much less of a dose..on Lantus, he was at 8u BID. He now floats around 4.5/4.75u BID of Levemir.
The negatives: The later onset and later nadir. If he's high, he'll stay that way for about 4 hours. That sucks. And for me personally, it's essentially impossible for me to get his nadir in the PM cycle, due to my schedule.
The neutral: As I mentioned above, the Lev has an ability in Fred to seriously yank him down from high numbers. But that can be scary if he's dropping too fast, too early. I know how powerful it can be in him, which is why I am generally very conservative if I see a lower number. I'm terrified of hypos b/c Fred does not really respond to carbs, and very minimally to Karo. So if he's down, he's down.
All food for thought!