1/4 HT easy. Display him with the sonar-head if the HS isn't improved. (although I think you could get a good pose out of him by using PERS, angling his pupils to the top of his head, and moving his neck down)
I've been having the 1/4 vs 1/6 dilemma rage in my head for months and months. I've settled on 1/4 for tons of reasons...
a) Presence/Detail/Realism/Wow-factor
1/4 scale pieces are inarguably better-looking. The way the clothes sit, the paint finishes, how they look under controlled-light. Hot Toys may not be upping their sculpting game as much as hoped, but their pieces will get better with time I'd guess. Meanwhile Enterbays T-800 is leagues ahead of Hot Toys Arnold-esque efforts.
b) 'Finality' - no need to collect 7x characters from a movie, just one or two will do at this scale. Stops you feeling the need to own 10 variants of Iron Mans suit.
c) Price. Fewer releases, mean easier to keep up with. Stops bad purchases that you end up selling later on. I think collecting 1/4s will work out alot cheaper than a 'collect them all' 1:6er.
The cons for me were space (inc. limited display options) having to pre-order to afford and waiting! Although i've seen a good looking cabinet on Ebay for a reasonable price that should hold 1/4s. In my book, you own less quarters than sixes, so the overall space a collection would take shouldn't be much more.