Latin is slightly easier due to not having to learn another alphabet and slightly simpler grammar, but if you have studied an inflected Indo-European language before, you should not find either terribly difficult. It was a widely-held opinion in Westrrn European education in the past that students should study Latin first, then Greek, but that was mostly due to the popularity of Latin in the West.
It really depends on what you want to read. Greek opens up the Septuagint and New Testament, the majority of the church fathers, classical philosophers like Plato and Aristotle, and classic playwrights like Aristophanes and Sophocles. Latin lets you read the Vulgate, Roman politicians, philosophers, playwrights (worse on average than Greek drama in my humble opinion), and poets, and medieval Latin works, which dwarf the entire Greek corpus by orders of magnitude. Latin was used for record-keeping, all Church business, and scholarly works until the 19th century, and the conservative nature of using a dead language with a fixed standard means you can read most later works without much difficulty.