I picked the Saracen and the Hunter
The Saracen is the best to me as its obscene speed, good armor, and solid weaponry give it an edge over many mechs when played in groups. It does everything that I want a non-mech force to do. Scout, provide LRM fire support, Flank, etc. So to me this is the best option, however from a practical standpoint hovers cannot do everything or keep up in certain terrain. Also they can't perform under fire as well as their tracked or wheeled counterparts. I have to pick the Saracen from the "most value added" and therefore "best" standpoint. Also a whole lance of Saracens would likely outperform a whole lance of any of the other choices on the poll by a country mile. That high THN plus the good range is going to be nasty. The fact that Saracens make excellent spotters for indirect fire and scouts takes the cake for me.
The Hunter is kind of a cheat because of the Fusion Engine, its cost is vastly higher than the others on the list and the Fusion Engine does make a big impact on its use. Definitely "on paper" one of the best vehicles of the era. However the high cost would limit its deployment in a "real" environment and make losing one more impactful. I can't vote against the Hunter because objectively it is way "better" than a choice like the LRM Scorpion. Yet, given the role of a procurement officer or a military commander I would definitely chose a lance of LRM Scorpions over a single Hunter.... The BV doesn't work out to quite the same numbers and generally I would argue that a single Hunter is worth 2 LRM Scorpions, so it beats out the Scorpion in BV based ranking. Also in a force where you are supporting deficiencies in your mech line with tanks (think all succession wars battles) the Scorpion is going to provide you with a capability that most closely matches that of a mechs. If I didn't have a LRM fire support element in my mech force a Hunter could reasonably fit the same role and wouldn't likely fall far behind a mech force.
Honorable Mention to the Striker.
Love the Striker and it is my favorite / preferred "guard the base" / missile support tank. Best? No.... but favorite. And the combo meal of the SRM-6 and the LRM's really does work to throw down against enemies at any range. Sort of like a Vehicle version of a Crusader, soften them up at range (hopefully with help from buddies) then close in and crit seek if safe. It's reasonable speed and armor keep it alive any time something with a higher "shoot me" factor is on the board. This is pretty often considering the low BV and "threat" of a Striker. I usually run them in pairs supporting heavier tracked tanks, left alone a Striker (or two) can seriously damage other units. The LRM 15 version is nasty too, especially with alternate munitions and when paired with more deadly MBTs can also be a real treat. Great tank!