You should be able to have success with just about any leeks in your part of the country. I'm in the South, and we have to plant them in the fall, and I've never had any problems with any of them. I like to grow Bleu de Solaise, and like it, but it's getting hard to find.

I did find a link below with the different types. However, there are a lot more types of leeks than these and I've never even heard of most of them. If you're planting in April, you may want an early variety that could be harvested before winter.

Here is a link that might be useful: Different types of leeks