It looks like you're pretty set already having unlocked some guardian weapons. But be warned there are Thargoids now that can destroy Guardian modules -- the Glaives. Also, entering Sol will slowly melt them just from being there. I'm not sure why you weren't able to work with the Chieftain, it looks alright to me.
I wouldn't really suggest either of your proposed passenger craft. Even if you ran shields you will want to upgrade those thrusters. They are very slow and you will get pummeled during a hyperdiction because you won't be fast enough to escape.
But I'm not a pro at Thargoid stuff. I've heard it helps to stay cold around them so I prefer to run shieldless. I also consider the simplicity of that a bonus; there's a lot going on and I like not having to bounce pips around to keep shield and weapon caps topped off. In light of that, I use:
This
FAS for combat. I am not good enough to solo much of anything besides scouts. If I'm in an AX situation with other people I relegate myself to scout cleanup duty, and attempting to help tickle the interceptor if there are no scouts.
This
Orca for passenger missions. Again shieldless because you will be hyperdicted 100% of the time trying to leave, so hitting silent running on the drop so the bugs can't target you means that shields are dead weight. Bulk up the hull instead. Orca because it's fast AF... >500 m/s cruising and like 630 boosting. Outruns FSD shutdown missiles every time. Ignore the guns on that, because they aren't used for fighting. This ship only runs.