I think that the "Diabetes Solution" is a more comprehensive look at Diabetes, and the "Low Carb Solution" is a more concise book that concentrates mainly on the (very important) diet component.
I haven't read the "Low Carb Solution" but (despite the criticism it gets here) the "Diabetes Solution" is a great book. I realise that parts of it are slightly out of date but, in the context of when he first wrote it, Bernstein is a visionary. He almost singe handedly invented the "low-carb plus testing" regime for diabetics, and as such many of us owe our health to him. I read it when I was first diagnosed, and I must admit I got a bit confused between T1 and T2 things.
I recognise his <30g a day (with no fruit) diet is not easy to follow (and the reason why he gets so much grief on forums like this), but if you can stick to it then your results can be outstanding. After trying a couple of different approaches, and reading every book on the topic I could find, I've come to the conclusion that <30g (with no fruit) is the best possbile diet for a T2 diabetic, as long as you can stick with it.
Once you've finished this, if you want some more insight into why low-carb and ketosis work so well, then I thoroughly recommend the "Art and Science of Low Carbohydrate Living" by Phinney and Volek.