It's really difficult to presume to know what Rajang might have preferred (no offence intended !) ..... I guess that would be down to his regular keepers to make a call upon, on the basis of any signs of stress etc. in each of the respective enclosures.
My gut feeling is that he'd prefer a larger space ...... his previous indoor area was very low ceilinged for example, and, from a human perspective, seemed very claustrophobic. Would orangs feel the same ? ......... hard to tell, but as they dwell in treetops naturally, I'd hazard a guess that they'd feel more comfortable in a loftier area, even if they were captive bred and had never experienced trees many metres high.
Looking at the new outside area from a privacy perspective, this obviously allows Rajang to go about his business without (ignorant) people banging on the glass (which makes me so angry, especially when accompanied by cries such as "that monkey is disgusting, look at his revolting hair" which I've heard more than once ...... though at least most people have the good sense to be fascinated and/or in awe of him), or being right in his face. Then again, I guess that wherever he was, he has always had the option of moving away whenever a sea of faces got too much for him.
As the weather gets warmer, it'll be interesting to see just how much he does go outside. If he does actually enjoy looking directly at people, a reluctance to go out might just be an indicator of this, if and when he realises (as I'm sure he will) that outside means no face to face contact. Conversely, if he spends a lot more time outside it might just prove he appreciates some time to himself.
I wonder if any Colchester keepers or directors read these forums ? ........ you'd think they would, wouldn't you, to glean feedback about their business and how their care of the animals is being perceived. Certainly, the lack of greenery must be relatively easy to address and would probably make a lot of visitors feel happier - and I find it hard to believe that Rajang wouldn't also show an interest in plants.