Which Loyalist(?) Legion fits to my intention of playstyle?

[Phoebus Apollon]

Hello friends,
Greetings from Germany first: I hope that you understand my words and that not too many mistakes creep in. It is all about:
I wanted to get into the Horus Heresy with some friends with the new edition - I've been reading the series since the beginning and absolutely love the setting. Since my people will all join Horus and his traitors, I will defend the throne - and be the only loyalist in our group. While I have a bias as to which legion I pledge allegiance to, I'm not completely sure. That's why I wanted to ask you guys for help on which Loyal Legion (or Traitor Royalists?) suits me best.
Playing style: I would like to play a more infantry-based army: Few vehicles (likely as an exception: dreadnoughts), not so much speed and similar gimmicks. I'm concerned with honest, tough infantry, which draws sword and shield on the brink of doom to defy the chaos. Gladly heavy infantry, gladly breachers, just such jokes.  I would like to play a slow army that focuses on shield-wielding infantry. Preferably two units of Breachers, plus maybe two more units of shield-carrying elite infantry (Phalanx Warders? Immortals? Suzerain or Praetorians?), supported by Terminators and Dreadnoughts. The number of units without shields should remain manageable, a maximum of one tactical squad and one or two units with heavy weapons. Plus a leader for the Terminators, for the Phalanx and maybe some Apothecaries.
I have no idea if such an army is competitive, to be honest it would be of secondary importance to me at best. She would have a good vibe on the field and that would count for me - even if I don't know how to open tanks at the moment.
Among the options that came to my mind:

Imperial Fists: I loved this Legion from the start, if only because Rogal Dorn is an idealistic Stannis Baratheon in Space. I find the Rite of War “The Stone Gauntlet” particularly exciting. Cons: The rather thankless color scheme and the fact that they must be quite popular?
Ultramarines: Great background, thanks to Abnett! Also: Who else remembers the Evocati during the Battle of Armatura? That's exactly what I find exciting - and with the Suzerain and their special shields they have the opportunity to reflect my intentions. Cons: Do they completely fit the playstyle?
Iron Hands: Depressed, fatherless warriors with forbidden necrotechnology on the path of vengeful self-destruction? bring it on! Cons: What is their playstyle like? In addition, the color scheme is thankless and boring.
 
Did I forget other legions? What do you think overall?
Greetings from Germany!

[Doghouse]

Welcome to the B&C.

 

Death Guard is another to consider for infantry armies.

 

For the most part you have chapters and companies of Legions that can lean to certain styles of warfare such as ship boarding or heavy armour so any of the three you have mentioned would be fine. Unless you intend to start other Legions then I'd go for the one that instantly stands out to you and you can bring yourself to paint or has rites and rules that appeal to you.

 

With what looks like rules that mean any Legion force can be Loyalist or Traitor this provides you with even more options. :)

[MARK0SIAN]

I think your best option is probably imperial fists for what you’re describing but I think it might be worth considering salamanders too. Their fire drakes carry cool shields and they can use breachers just like every other legion.

 

They also really fit that idea of tough, survivable infantry and dreads. They can work very well in zone mortalis games too, although I’m not sure what that will look like in the new edition.