I do like the neon-dark atmosphere of your picture, so I will drop my two cents in the hope it helps.
First off, to me the building has the appearance of an office complex, most likely tied to administration and/or financials. As such, quite a few of the subsidiaries you named would fit quite well. For Architectural Dynamics, however, I would (intuitively) expect a more eccentric architectural design.
So I had to start thinking - why would a security outfit for another "corp" respond to the explosion (I plan on having security running across that walk bridge)....they have to be connected somehow esp with the closeness.
However, I guess your thoughts revolve around who might plausibly respond to such a situation. I would tackle that question from a different angle: Given the recentness of the explosion, one option would be: no one. The event just occurred, and response takes time, so there may not be anyone on the scene yet. The streets might just be as deserted as they appear now.
That said, one could also assume, that prior events (e.g., a violent confrontation preceding the explosion) attracted attention and/or triggered alarms. In that case, multiple parties may show up to the party, independent of which corporation resides in the building:
- Lone Star or Knight Errant could react in response to panic buttons being pushed in the general vicinity. They might also ward off larger sections of the area if prior events dragged out over time.
- DocWagon may initiate an aerial high threat response due to clients signaling distress or life threatening conditions from inside the building.
- One or more news outfits may show up early if they caught wind of what is happening.
- Not all corps provide their own security. An outside security provider, such as Knight Errant, would be entitled to a response on premise.
- Fire fighters may already be on the scene.
- Random onlookers might even be the most common sight on the street.
In essence, I feel you have quite a lot of leeway as to the choice of the corporation and the responders, depending on how the story behind the explosion plays out in your mind. You may also want to convey an atmosphere of confusion, bickering and chaos resulting from unclear jurisdiction and general jumpiness.
Personally, I might opt for Hypersense, since tech companies make such a tempting target for corporate espionage (the name alone conveys an aura of high-tech). In my opinion, that caters well to the general atmosphere of Shadowrun.
One thing to keep in mind, might be the Shadowrun timeline. There is a chance that anyone of the named subsidiaries is gone by the time Horizon flourished.