Hmmm I think I see where this is coming from
So let's walk through each of these.
Hover Tanks (FE)
Solid, all-around units. They're heavies, and deal decent damage and have good health. Good movement and range, and have the force field ability, so damage done against them is reduced. The key for Hovers is that they hide on plains. Plains is one of the most common terrain types, and that makes the hovers essentially untouchable except when a unit is right next to them, or when a unit has an ignore stealth ability. Works well with 7 rogues, whether in auto or manual. Since the tiles units start on are always plains (fun fact), your hover can never be hit in the first round of the battle unless a unit has an ignore stealth ability.
Recon Raider (AF)
Ok units at best. They're fast units, and deal ok damage and have relatively low health. Movement is high, but that's to be expected, so the lower range stat is understandable. However, their ability is Dug In, where they take have a defense boost when the enemy is farther away.... on a fast unit. The increased movement speed and Dug In ability counteract each other, and the AI turns these guys basically into suicide units. For autoing, it's useless. Give them a couple turns and they'll rush the enemy and die. Just don't use these for fighting.
Surrogate Soldier (AF)
Decent units when used right. They're ranged units and have low-to-mid damage and health. Movement is pretty good, and they have a decent range. What's nice about these guys is that they have the Dug In ability (on a ranged unit so they aren't trying to rush the enemy!), and the Contact! ability. Contact! is really nice, since it means that the enemy will be taking lots of damage when they attack you. These would work best when held back manually, just to ensure they aren't killed first-round. However, they lose their quality with their lower stats, and shorter range (same range as MG Teams, 4 eras before!). Just use them carefully if you use them at all. I sometimes use them for defense or the PvP Arena defending army.
Battle Fortress (AF)
Decent units, sort of. They have higher stats than hovers, including more movement. They also have the Reactive Armor ability, which means that they take at most 3 damage (unless they are attacked by a unit that ignores Reactive Armor). Sounds great, right? Well, no. They don't have stealth, and that's the biggest hit against them. They can be hit by artillery easily and can be attacked anywhere on the map as a result. Also, that Reactive Armor ability is ok at best in reality, since against units with strong boosts they'll die within 4 hits. Force Field would have been better.
Conclusion
So, long story short, Hovers are best here. The Recon Raiders are basically worthless, Surrogate Soldiers have their uses when you have to fill out a defending army, and Battle Fortresses just don't hold up in practice, but aren't completely horrible. The Force Field ability is awesome, since even when you take what would be 3 damage, it's reduced to 1. That means that it's a lot rarer to see your hovers get heavily damaged from one battle, whereas you could see that with almost every other unit. This lets you attack faster and with less damage than almost any other comment. Just watch out against the units that ignore stealth, including Plasma Artillery. If you got them in a lower age, it can be easy to lose them if you are against those units and click too fast (speaking from experience here).
And that should sum it all up lol! Hope this helps.
[Edit] WOW I write too much lol