I honestly expected this thread to go further, taking about successful equipment combinations.
I like the Pillager as a base design as it combines Jump Jets, long range Gauss Rifles, and energy weapons. Its missing Missiles and it can only use all of its weapons at less than half its maximum range.
The Mad cat Mark II furthers that design as its clan technology means its energy weapons and overall the entire design is longer range, its faster and 10 tons lighter.
Missiles and Energy weapons are easily compatible. Its easy to back up some long range energy weapons with ShortRangeMissiles and use LongRangeMissiles with medium range energy weapons like Medium Lasers. Ballistic weapons are more difficult as they are just so heavy and the damage differences between models is massive. Converting from different Models of LRMs or SRMs is easy but changing from and Ac-5 to and Ac-20 is a drastic design change.
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Differences between the Mechwarrior games and the tabletop change things heavily. What works on one probably wont on the other. Jump Jets are very useful on the tabletop while in video games they are overrated aside from Mechcommander where they are very useful. Technically aside from some obvious improvements from clan technology there are no "bad" tabletop designs, just ones that are situational.