I'm coming in to offer my take on this
First, as far as I can tell PS3 Tears to Tiara 1 has the same rewrite amount as PS2 Utawarerumono. That is, everything already written on the PC version is unchanged, while a few stages are added and a new subplot written in (and quickly resolved).
PS3 version should be treated as a new game because it's TBS, not PC's RTS, but as far as the story portion goes, it should be treated as more-or-less the same.
I can see why one might like Tears to Tiara 1 more, so I'll give my personal take on this, ranking Aquaplus' RPGs from favourite to least. Note I'm talking about story only.
Wall of Text Warning! Skip to conclusion if you don't need details!
Tears to Tiara II is definitely my favourite. But I echo hellish in that the ending isn't as strong. Quality wise it sort of starts off high, then steadily climbs until it reach Mt. Everest Level at the half way mark, before jumping onto a plateau and wobbles a bit, before climbing high again but never reach what it was before. The story after half-way is also less relatable. The second half has one or two too many cop-outs, making the ending bland except for the voice acting, which alone rescues the part.
So why is it my favourite? It is an epic literature. It dumps the harem (I like harem, but I'll explain later). The story has two themes: religion, and sacrifice. The first half is almost entirely the latter, and is so well written that on second reading even some really small things like mannerism of the villain that was easily ignored on first reading becomes clear that it's actually foreshadowing the twist. The second half turns up the theme of religion, and becomes philosophical, without getting in the way of the story. The first game clearly says "Religion is Bad". But this one asks "Or is it?". It asks also "What's the role of religion in a society" and even at the end never gives you an answer. If you like thinking, as I do, this is bunch of extra points for it. Of course if you don't care for it, then all it does is slow down the story. Then, going for epic, the story drives for scale and politics and awesome. It's good to see once in a while a military genius who can walk the walk in fiction, not just make up stuff that wouldn't work irl half the time. I have to echo Hasdrubal's CV in his commentaries after the end in that rather than a game plot, TtT2 reads like heavy literature.
And as a history buff, this one has a lot more references.
Utawarerumono comes a close second. In fact I am really torn on how to place these two and could easily place Utawarerumono first.
Utawarerumono has basically no themes and no philosophy. It is not an epic, and the plot is straightforward(-ish). But it goes for the other path. The story is written as in-universe "normal" people get thrust into situations good and bad that they have to respond to. It has the best comedy, the best slice of life parts (TtT2 has none), and even its harem in a way makes sense, which is super rare in a VN. It successfully builds and fleshes out every single character, where both TtT games only does this for a handful of main characters, and this makes all the characters extremely relatable from start to end.
It is basically the best telling a "traditional" harem, personal-relatable romance story in a RPG setting. As such it starts high quality and keeps it all the way through.
Finally, Tears to Tiara I
It is last because it's really obvious that the author is trying so hard to write an epic (TtT2 style) but doesn't get there. It has a very forced harem. Harem itself has no place in an epic, just like love-triangles has no place in a war movie. All it does is take away screen time from the epic plot. And thankfully the harem drops off as the female cast stops being haremettes and starts being soldiers, improving the quality of the story steadily, and just demonstrates that the harem was redundant in the first place!
The writing itself is a bit barebone, and many of its attempt at slice-of-life falls flat. Where-as Utawarerumono fleshes out the entire main cast and many side ones, and TtT2 fleshes out its 2 villains and 3 to 5 of the main cast, TtT1 fleshes out only the two male protagonists (PS3 at best fleshes out 2 more characters). This fleshing, however, is very well done. Its theme of comradery is easily relatable. And this part does have a lot of epicness to it.
Once they enter the last arc of the story, however, the quality drops off again as the protagonists finish their development one arc too early and neither the supporting cast nor the villain picks up the slack, turning what was an original story very traditional, which while not mattering to a lot of people, gets it ducted points in my books because it doesn't do what it strives to do. My biggest grip with this work is that the plot naturally lends itself to some philosophical musing, yet through one single line before last boss, the author recons the villains' motivations already previously established for something traditional and cliche.
It pains me to say this but IMO the anime version is superior to both PC and PS3.
In conclusion/Tl;dr: Tears to Tiara II - Heirs to the Overlord is an epic. Utawarerumono is the epitome of transfering a personal, slice-of-life romance into an RPG setting, and Tears to Tiara (Garlands of the Earth included) is basically the author not having enough conviction to abandon traditional VN story telling in order to tell the story that he wants to tell. It wants to be an epic at the same time as a traditional VN harem slice-of-life, and doesn't quite get both right. So I am really glad he has taken the step and dumped most of the unnecessary things to tell the story he wants to tell for Heirs to the Overlord.
As for why I put Tears to Tiara II above Utawarerumono. I will admit Utawarerumono is more emotionally moving and relatable.
However I have always been of the opinion that Visual Novel is an art form with way too much untapped potential. It combines the best parts of novels, picture books, and screen, without having to take on a lot of their flaws. Therefore it can be used to tell all sorts of story, better than any of the other art forms. But it's burdened with its origins of being made for harem h-games, so too many authors feel they must make it at least a harem, slice-of-life story to satisfy their target demographics. So when a work like Tears to Tiara II comes along and says willingly breaks boundaries and takes risks to tell the story it wants to tell, even if it ends up not selling well because of it, it should be applauded.