Looking for input on AUX Questoris Freeblade loadout

I'll be attending a semi-competitive tournament soon for which I'm planning on taking an Super-Heavy Auxiliary detachment with a Questoris knight to complement my AoO detachment of Sisters of Battle (argent shroud, mix of shooting and melee). I'm well aware that this is not the most competitive choice, but I'm somewhat limited by what I'll be able to get painted before the event. I've looked into the books and tried a test game now and I'm thinking of either a knight Warden or Errant with Mysterious Guardian so I can protect it turn one in reserves and still be effective when it's my first turn. What I'm unsure about is the loadout of the knight.

I am now doubting between a Reaper Chaincannon with Thunderstrike Gauntlet or a Thermal Cannon with Reaper Chainsword. I like to have a mix of 'horde' and vehicle/monster clearance and be (somewhat) effective in melee and shooting while operating separately from the rest of my army, hence these choices. Because I have the points for it, I'm also taking the Stormspear Rocket pod.

I'd love to hear your input and experience on these weapon choices or other suggestions with respect to an AUX Questoris Knight (I only have the standard kit for loadout purposes). The Gauntlet has an interesting profile, but only 4 attacks may be too much of a gamble when trying to kill bigger stuff. I noticed yesterday that invulnerable saves can be real swingy when you only have 4 attacks that hit on 3+. This made me think that the Thermal Cannon + Chainsword may be the more versatile option.

I expect that there will be Guard, Daemons, Death Guard and Necrons present at the tournament.