Since you didn't provide any specifics about the criteria for comparison, I'll start with my three rules for analysis of data:
1. plot the data.
2. Plot The Data.
3. PLOT THE DATA.
But which plots is highly dependent on the type of data you have (continuous, count, text, ordinal, etc.)? Is time ordering of the observations relevant? Do you have missing, nonsense, or other suspicious observations in the data? And other questions...so if you can provide some more details regarding the data and the specific criteria for comparison, then perhaps we can offer guidance?