If you're going to read one article on ActiveRecord vs Data Mapper let it be this one by Matthew Machuga.

The next time you come across the ActiveRecord vs. Data Mapper argument, or ones like it, be critical of what is being said. If it impacts your work in some way, do some research to find out if what is being said is true or if it has been something lost in translation. Don't feel bad for using a pattern that has spread across multiple languages and ecosystems successfully, and is probably the reason we have most of the web frameworks we do today. While the ActiveRecord existed well before Rails, it was Rails that gave it a beautiful API and made other frameworks like CodeIgniter, Laravel, .NET, Fuel, Django, etc want to have something comparable. If you use Eloquent, ActiveRecord for Rails, or any other AR ORM, make sure you know that you are not alone. You are in good company of many, many developers who use it successfully day-to-day. However, if one day you choose to use a Data Mapper implementation or something else, then you will still be in good company, and still deserve respect regardless of which side of the fence you fall.