BU's anti-BOW work is simply the public side of the corporation. It's true purpose is the creation of a new world order where only the strong survive, as they say in UCorps. Remember, this was originally Wesker's group.
The team with the red logo is just an elite unit, like the USS, not nessesarily the entire dark side of the company, which reaches to the leadership level.
We don't know exactly how they operate yet, but they need to dominate both sides of the conflict. That means fighting BOWs and contributing to their creation.
T-ALOS's purpose was different than the original Tyrant concept. Tyrants were supposed to be unfeeling, intelligent super soldiers that could blend in with regular humans. Imagine a pursuer like the Nemesis T-type that looks like a regular person - it would be perfect not just for the battlefield, but assasination and infiltration. Umbrella's last attempt at making human-like Tyrants was with Hypnos, but with it and Sheena Island destroyed, they lost that line of research, and their desperate situation meant they could'nt just start over.
T-ALOS was an attempt to create a Tyrant with unsurpassed efficiency in combat against armored vehicles and multiple combatants. It dropped all sublety in favor of raw power. It wasn't a route they originally wanted to take, as cybernetic enhancements take away from the point of BOWs (weapons that can cheaply be mass produced via cloning).
Ustanak was created by using a rare host who was highly compatable with the C-Virus. While it had regenerative potential and intelligence surpassing even Nemesis, it looked no more human. With the only specimen destroyed and it's creator dead, it's unknown if it can/will ever be reproduced.
HAOS was a doomsday weapon, and it's sole purpose was to wipe out all life on the planet.
The pustule masses created by Uroboros are completely uncontrollable and pose a massive risk to the planet if used. Uroboros adapters would be immortals surpassing anything else seen so far, but they would retain free will and be of no use as weapons - just as evolved humans, like Wesker.
The Mold has the potential to be the perfect weapon, able to quickly and quietly subvert entire armies without even directly engaging them. Mold Thralls retain their human forms and can gain near immortality, like Tyrants were supposed to, but a side effect of infection is insanity and extremely sadistic tendencies toward themeselves and others. Even more problematic, control is limited to Subjects like Eveline, and there is currently no reliable way to control them, so the Mold needs further modifications to be practical.
Besides controlling armies of infected, the Mold can also create unlimited numbers of Molded.
Morpheus' electric shield gives him an advantage, but once that is penetrated he is just an unstable Tyrant. Kodoku Tyrants are especially tough.
Tyrants retaining intelligence and even personality isn't rare at this point, between Ultimate Abyss, Sergei, Diego, Niel, and Morio.
It depends on what you have in mind when looking for "the best". If you want viruses able to wipe out all life on the planet with no regard for user safety, then t-Veronica, t-Abyss and Uroboros can do so when released in an ideal enviroment, while HAOS was created to specifically spread C to everyone.
If you want an obedient army, the Javo created by C are reliable and powerful, yet the distribution of Anti-C makes that difficult, and so until a new strain emerges or the Mold is perfected, Las Plagas is your safest bet.
For presice assignments, bodyguards, and recovery missions, you can't beat Tyrants.
For killing off outbreak survivors holed up in secure areas, Hunters are still efficient, particularly the Farfarello, but it's extreme aggression makes it unsafe.
For wiping out certain and presice numbers in a population, try the a-Virus, but again, a vaccine now exists for public use.
If you don't want to kill people, but want to become immortal, Uroboros is the most powerful, but it's extremely low adaption rate means it will probably kill you, so conquering your fear with t-Phobos or taking a 15 year nap with t-Veronica is safer.
Taking everything above into account, the most well rounded, practical weapon is the C-Virus, unless the Mold is perfected, which would render all other BOWs pointless.
The most powerful mutant creature seen in regards to survivability and recovery would be Albert Wesker, followed by Jack Baker (and probably Eveline), HAOS, Ustanak, and maybe Mutant Simmons. Lisa inherited immortality from Progenitor, but to what extent is hard to say. The enhanced healing granted to Tyrants by the Nemesis parasite is obviously worth mentioning, as are G creatures.
HAOS, Eveline, Uroboros Aheri and V-Complex posed the greatest biohazard risk.
