So you are looking pre-Jihad . . .
For the Clans that means Elementals, Salamanders, Gnomes and maybe Sylph & Golem- understand that for most of that time its the Elemental.
For the IS you have the GDL Standard & Scout, IS Standard & its factional flavors of Cavalier/Raiden, Infiltrator Mk I & Mk II, Sloth, Fenrir, Kage, Kanazuchi (or whatever), Achileus, Longinus, Fa Shih and Purifier. Of that the Infiltrator Mk I and Sloth are generally felt to be duds, but they may perform better in RP than TT. Once you are near or at the Jihad the Phalanx, Trinity BAs, Grenadier, and a few others become available.
The Cavalier (SRM) is the ONLY IS suit that jumps with a missile launcher . . . because its in the arm.
Medium BA are the generalist designs, with the best IS ones of the era being the Infiltrator Mk II, IS Std/Raiden/Cavalier, GDL Std, Purifier and Longinus being the top in the field. I put the Longinus last because it mounts a backpack SRM2 launcher which restricts it to the walk of 1- it needs transport or to fire its SRMs to move faster.
GDL Std will be superior in a city because its movements will not be inhibited by the buildings
For IS vehicles of that time frame . . . it depends on what you want them to do.
As someone said the Myrmidon is about the best line tank, it has a PPC on a turret, good armor & moves 5/8. For campaign play it has a SFE which means you do not have to worry about the fuel so it can travel with mech forces without needing refuel like ICE vehicles.
And while there are a lot of Vedettes, Scorpions and Weapons Carriers (AC/2, LRM, SRM) in canon they are typically 3rd rate militia forces . . . so unless you are fighting off a swarm invading Podunk you will not be seeing them fighting a regular unit. If facing the Capellans you might consider the Po Heavy Tank in the same category.
With TW rules changes heavy and assualt tanks are no longer BV sucking wastes waiting for inferno love. Which means that Alacorn VIII is great in the backfield for killing other heavy armor or mechs. Following the paradigm (slightly mobile pillboxes) would be vehicles like the Schrek, Gurti, Demolishers and a few others.
Best hovertank is probably the Regulator . . . movement with a BFG on a turret. Its range makes it acceptable since it can stand off a bit to keep up the movement mods against a target while still having minimal targetting penalties.