Plan your approach
They all have their nuances and as such need to be treated with different study techniques. Are they wrote learning ones, assimilation ones, ones with equations and problem solving or do they test your ability to find something in a text? Depending on how good you are at each of the above styles will be the decider on how hard (or easy) they are.
That being said, the subjects themselves and the content within are not by any means complex. It comes down to your ability to be belt fed masses of info, decide what is important, then be able to regurgitate it.
There are degrees of difficulty however, which is why you need to plan the order in which you do them.
I did HUF, MET, NAV, PER, PLA, SYS then LAW……this worked for me and they seemed to build on each other fairly well.
The hardest for me was Sys simply due to the mass on info…..followed by planning (primarily due to fat fingers and little buttons on the clac).