A: Start by listing your requirements in order of importance.
This is a pretty common problem that many retailers face; with so many technologies that span such a wide range of costs how do you figure out what's right for you? Well you should start at the beginning: what are your specific needs and what is your budget? Defining the answers to those questions will make your search much easier. I know this sounds like common sense, but I'm talking about actually listing out your needs (and ranking them in order of importance to you) and you will better be able to see which solutions best match up to those needs. As you go through this process you may find out that something you thought you needed isn't actually all that critical or that it can be met through some other solution. There are a number of great resources on the web for looking at the various technologies out there, but I'd recommend the Solution Finder at www.ecommerceknowhow.com where you can filter technologies by type (including shopping carts and e-commerce platforms).
With regard specifically to recurring order functionality, this is a fairly common piece in modern e-commerce platforms. Without knowing your budget or current setup it's a bit hard to recommend anyone specifically, but I can say that platforms like ShopVisible, Weblinc, Jagged Peak, Order Dynamic, and Nox all have recurring order capabilities. There are also some 3rd party services such as Order Groove that you integrate with an existing cart/platform solely to achieve recurring order functionality.
Depending on your current setup, you may also be able to configure recurring orders through your payment gateway.
It all comes down to balancing what you need to conduct your business efficiently vs the cost to do so. Good luck in your search!