Quite simply the Grade 1's are the best in terms of squareness and condition.
The Grade2's are also a very good Reclaimed Railway Sleeper but will contain some defects and will not be as square and uniform as the Grade 1.
The lowest Grade that TimberClick offer is the Grade 3 which will be far more rustic, contain more splits and irregularities.
When choosing which of the 3 Grades to buy you need to decide upon the end use and the appearance that you wish to achieve.
Some expamples are as follows:~
Grade 1 - Retaining walls, raised beds, steps, curbing and edging.
Grade 2 - similar to the Grade 1.
Grade 3 - Ideal for raised beds and retaining walls where the aim is to produce a rustic effect. Particularly useful where part or all of the sleeper is hidden from the eye, ie bases for sheds, edging or curbing where part or all of the sleeper is embedded into the ground.