> is it all the same or are there different types?
Stick with DOT 3 or 4. Do NOT use DOT 5 as it is incompatible with the DOT 3 or 4 that came in you vehicle.
DOT 4 has a higher boiling point than DOT 3 and is generally consider better than DOT 3; however, some people believe DOT 4 is more hygroscopic than DOT 3, and therefore needs to be changed/flushed more often. I generally just use a name brand DOT 4 fluid, which often is labeled as DOT 3/4.... there is no difference between fluids labeled DOT 3/4 vs. DOT 4, as every DOT 4 fluid also meets DOT 3 requirements.
And yes, there also is something called DOT 5.1 out there which is completely different from DOT 5, and is compatible with DOT 3/4 fluids/systems, but there really is no need to consider expensive DOT 5.1 unless you are racing.