Most of my stories along those lines are about playtesting my own designs rather than cannon ones. The one that comes to mind the most is about a 100 ton clan assault omnimech I designed. The variant I liked the most on paper had 4 Large Pulse Lasers+ a targeting computer, 4 Streak SRM 6s, and just enough heat that it wasn't over-sinked but didn't have any serious heat issues. It performed okay, but it wasn't spectacular for me, doing about as expected.
One of the other variants of this omnimech though, had a gauss rifle, LB 10-X AC, Ultra AC 10, targeting computer, and a bunch of LRMs. I thought the weapons were eclectic and the mech just didn't feel very cohesive to me, until I used it in several battles and it's performance pretty much amazed me. That design taught me a lot about the value of different systems working well together.
As far as Canon stuff goes, my favorite warships are the Kyushu, Soyal, and Night Lord. I don't think I have seen anyone give complementary reviews of the first two, but I get them do work out pretty well for myself. A lot better than people seem to think they can.