Depends on your playstyle, if you like rushing and taking damage for the team you should use bastion. But if you like taking cover and minimize damage taken you should stick with aegis.

I still prefer bastion

Bastion seems like the kind of mech best for offense and offense orientated defense, it is very good with 2 different times of weapon and high damage weapons alongside supressive weapons such as miniguns. And if you can't counter seeker, than its the perfect mech. (in my opinion)

Aegis is best for pure defense for yourself and your allies whilst also allowing for you to take ground slowly by advancing and than placing your shield. Its best used with long rang weapons such as sniper weapons and guided weapons alongside mortars. Combo weapons are less useful on this mech but can still be useful such as using mini gun alongside either guided missle weapons, mortars or grenades to bypass cover to a degree. it can help against seeker mechs but not as much as bastion. (in my opinion)

I think if you watch most content creators you'll see them using Aegis and not Bastion.  Weapon damage has gotten to the point that the Aegis dome is worth more than anything Bastion can put up.

The choice is yours.  :)

The fact that this conversation continues to be had between a legendary and an epic mech is exactly what the game needs more of.  Diversity of choice.

I personaly think aegis is a s tier mech, much better than bastion, tho i did get the bastion from the crate as well😉