The approach depends on if the vehicles support a mech force or if the vehicle force is expected to fight on its own.
If supplementing, then I think Getz has the right of it. Vehicles are much more fragile than mechs. You want your mechs to focus on the line fighting while your vehicles fulfill roles -- specifically fire support, ambush, and recon -- that keep them out of the worst danger.
This is my current go-to vehicle support company:
Fire Lance
4xPartisan (LRM)
Ambush Lance
4xPredator
Recon Lance
4xPegasus (Missile)
The Partisan (LRM) delivers 60 LRMs per round on a 3/5 tracked platform but is much better armored than LRM Carriers and similar fire support tanks.
The Predator is a 5/8 tracked tank with an AC/20. Lightly armored and with no turret, it's a classic tank destroyer, good in the shoot-and-scoot role. I like it better than the Hetzer because the Predator is tracked and faster. The upgraded version goes 6/9 and carries an LB 20-X AC.
The Pegasus (Missile) throws 18 SRMs a turn on a 8/12 hover platform, effectively making a pair of these a much faster, better armored, more survivable, and more flexible SRM Carrier.
Depending on the terrain and situation -- hills and spotters for the Partisan (LRM), constricting woods or buildings for the Predator, or open plains or water for the Pegasus -- each of these lances would be a good complement to a mech company.
But together, the combo is also a decent mix of fire support, hole-punching, and critting for taking down enemy mechs and other units. They are somewhat vulnerable without friendly line mechs, but their speeds also complement each other, with the Predator or Pegasus able to fall back to protect the Partisan (LRM) and the Pegasus able to swoop in and finish off a foe struck by the Predator.
This company also makes the most of specialty ammo -- mine-laying Thunder for the Partisan (LRM), armor-penetrating (AP) for the Predator, and fragmentation and inferno for the Pegasus.
If the vehicle force is expected to fight on its own, then you want main battle tanks that can quickly punch and exploit holes in enemy forces at range, while surviving long enough to do so. Here's my current go-to lances for an independent vehicle force:
Assault Lance
2xBrutus
2xZhukov
Battle Lance
4xManticore
The Brutus/Zhukov pair is a nice mix of LRM fire support, AC/10 and large laser hole-punching, and SRM exploiting that will quickly take down a mech on 3/5 tracked platforms.
Against faster opponents, it's hard to beat the well-rounded PPC/LRM/SRM capability of the Manticore on a 4/6 tracked platform.
You can play with even faster, non-tracked tanks -- like the Striker, Saladin, or Regulator -- in these line battle, cavalry, or skirmish roles. But my experience is that their higher vulnerability to motive hits and lack of mixed weaponry makes them one-shot wonders rather than reliable combatants. Mechs are really better in the 5/8 or faster battle, cavalry, and skirmish roles.
Lastly, by keeping them completely off the mapboard or out of reach, the ideal roles for vehicles are artillery support and spotting. The durability and firepower of mechs are wasted in these roles, and there are any number of artillery tanks and spotting VTOLs that can fulfill these roles more effectively and cheaply.
Hope this helps.