Dear Iñaki and all,
This is my opinion and current position.
No doubt that activating and qualifying summits with a 2m HH is the most effective way in terms of lightweight and minimum time to set-up and pack up, thus allowing an activator to maximize the number of summits activated and activator points bagged in each outing.
But activating with a 2m HH doesn't have the enjoyment of managing a pile-up on HF, both on CW and SSB, as well as having the great chance to regularly exchange greetings with many people across the continent and even the whole world.
Of course one can do both, activating 2m FM to QSO and exchange greetings with the local and regional colleagues, which is really nice, and do it also on HF to have the above mentionned enjoyment.
Problem in my case is that activating VHF and HF would require me longer time to remain in the summit unless the HF time was reduced to favour VHF activity and this is something difficult for me right now on the one hand, because I cannot extend my time in the summits, as I'm already pretty much always in a rush due to being a husband with 3 young kids to attend. On the other hand, because I enjoy so much HF activity that I would like to have them longer, rather than shorter.
Activating on 2m FM is an important battery consumer and this was a reason for me to stop doing it with my FT-817 in the begining, when I was using a 4.5Ah SLAB.
Activating with a 2m FM HH is, to me, far less fun than doing it with an HF rig with which we can use different bands and modes, allowing us to test propagation condition variations across the bands and time/seasons/solar cylce years, which is highly interesting at least to me.
Another important reason for me preferring HF activations rather than V/UHF ones is that the enjoyment and satisfaction that I get after logging 30, 40, 50, 60, 70 or even over 100 QSOs with colleagues all over the world can't beat a VHF log with perhaps 4 or 5 QSOs logged after several minutes CQing, or even less than 4 QSOs, as it has come to me (and you too) sometimes and then returning home with our mountaneer half happy but a rather frustrated and disappointed ham radio and SOTA activator half for not having qualified the summit after the time and effort spent.
It's pefectly possible to locally promote SOTA by being in touch with local and regional colleagues on the HF bands. I do it regularly.
However, it's very nice being able to chase an activator with a 2m FM rig in the car in a weekday at lunch time, as it came to me (and you too) this Monday when we managed to chase Juan-Carlos EA2EEB from the road while he was activating the 10 pointer Bisaurin EA2/HU-057 (2670m)
and that was possible because Juan-Carlos EA2EEB activated on 2m FM. Thank you!
In the case of a V/UHF challenge, I thing it may well bring some increase of activity during the time of the challenge but evrything would return to the current situation once the challenge would be over. See what happened with the 12m band: plenty of activity during the challenge and very little to almost nothing right now.
The chances to make QSOs on HF are so much more compared to those on V/UHF that it's just obvious why people prefer HF.
All this being said, I'll keep chasing on 2m FM whenever possible but I don't think I'll activate on VHF as long as I can do it on HF and I have limited time to remain in the summit.