In the interests of convincing a vote, I bring to you our opponent, the
Environment. And difficulty modifiers. As I know, mine is moderate, the other two are moderate-hard. Modifiers mean some traits may not work as well or be vestigial, or have a low evo rate. For Locusts trying to move straight to a ranged attack on a scout for example.
In the Misty Ravine, acid rain and runnoff are a thing. Rozers can make caves, Crabs can protect nearby units. In case of needing to cross, grubs can just climb down, crabs will have difficulty following. Rozers can just build tunnels for such forces, digging a slope down. As our main opponent is the environment, both serve a purpose.
The the Desert of Glass. This place has explosions sometimes. Crabs are meant to inhibit explosive reactions. Rozers build dens that are protected. Crabs have the edge for travel, Dozers have the edge for shelter. One thing to note is Energy, explosions are instant, so Crabs will need to keep it going all throughout, and won't get much in the way of rest. Rozers allow resting places.. The two definitely complement each other for this terrain, as in the Misty Ravine.
The Shattered Badlands. Nothing for the crabs to protect from, other than machines coming to life and crushing our grubs by the hundreds. Here, Rozers have an undenable advantage, as underground burrows out of sight will help survival. However an issue comes to fore, sight. In this regard, neither have an advantage, and it actually goes to the Locusts, who can find paths through the Misty Ravine and act as forward scouts.
Now we move to the next areas. The Bog is toxic vapors, Crabs have an advantage over all others for survival.
The lava rivers are hot, Locusts have the advantage here. But Rozers have revisions to their building ability available. 2 revision per turn means we can spare one for biological heatproofing of their construction.
The Glowing Crater is a case of none of the three having advantage, other than the Rozers able to build underground shelters where gravity shifting won't matter.
The Parasitc Forest. Locusts are out of contention here. Crabs and Rozers are in. Mostly through use of revisions.
The Dried Seabed. Once again, Crabs and Rozers. Crabs with cool gas, and Rozers for building underground warrens.
The Howling Crevasses. Locusts are dead, and require evo or revisions. Crabs aren't really suited for it, but evos will be useful for heavy defensive hitters. Rozers can build shelters. Though one can argue a lack of defense(though they do have chitin production for that) on Rozers, Rozers also have a evo lined up, a tunneling worm of great size which can help with travel safe from above, and swallow foes from below.
Of note, a Psionic Core for our grubs as a revision, to grant them about 6 foot radius of sight though feel. This would allow further children to have it developed further, the crabs for example. We may also develop the hive mind further through an offshoot evolutions. I am particularly interested in the Unforgotten as such a path as overseers.
So this is my argument for Rozers first. They don't need sight to build, and will be useful in every area. They also are a good starting point for supporter evolutions. No matter what we decide to revise for the Grubs, they are unaffected by the change, where the others will likely have an easier time with a psionic core. Any that evo from the Rozers can acquire benefits from the improvements to the grub even if the Rozers didn't have it.
And to the locusts, I would suggest removing the attack option and focusing on the actual role of flying scout for the first evo. I still think Rozers are the best first starter though, followed by crabs. We can grab scouts next to fulfill a trinity of shelter, offense/defense, and scouting. Survival is most important.
I am also really interested in the Rozer's + form it will get. It may develop some form of manipulation on it's own. Or some advantage when it comes to building.
Also of note, update soon if one option reaches 4 or 5 votes. Alpha seems mostly done.