首先说明这是两种不同目的的考试。
LSAT: Law school adimmsion test. 是针对进入法学院的考试。考试范围如下：

There are three multiple-choice question types in the LSAT:
Reading comprehension questions measure the ability to read, with understanding and insight, examples of lengthy and complex materials similar to those commonly encountered in law school.
Analytical reasoning questions measure the ability to understand a structure of relationships and to draw logical conclusions about that structure.
Logical reasoning questions assess the ability to analyze, critically evaluate, and complete arguments as they occur in ordinary language.

GRE: Graduate Record Examination. 在很多英语国家特别是美国，GRE成绩被作为研究生录取的标准之一。如今在欧洲，也有越来越多的大学，如德国，瑞典的大学，把GRE作为英语授课课程录取标准之一。考试范围如下：
Verbal Reasoning — Measures your ability to analyze and evaluate written material and synthesize information obtained from it, analyze relationships among component parts of sentences and recognize relationships among words and concepts.
Quantitative Reasoning — Measures problem-solving ability using basic concepts of arithmetic, algebra, geometry and data analysis.
Analytical Writing — Measures critical thinking and analytical writing skills, specifically your ability to articulate and support complex ideas clearly and effectively.

从考试目的和内容可以看出，很难比较哪个更难。简单说，如果你量化好些，就觉得GRE容易；如果你语言及逻辑好，就觉得LAST不难。但不论怎样，不论难与否，你的求学目的决定了你必须参加的考试。