I returned a week ago, staying at Blue Lagoon (BLR) two weeks all up.I honestly don't get why people go all the way to truk don't just spend a little more for the master or odyssey. the blue lagoon is bottom 3 of all places i've ever stayed, up there with a hostel that doubled as a homeless shelter in the UK during the pandemic and the airbnb in romania that looked nothing like the pictures where I thought I would be kidnapped and have my kidneys stolen. i've stayed in 10 dollar hostels in southeast asia that were in better shape.
The OP specifically asked about land based - in which case there's only two choices, and Blue Lagoon I feel provides the much better setup and location for diving, which is why you go there in the first place, right? Dive shop and dock is right there on site, as close as you get to the dive sites. Dive guides, fantastic.
If you were a single tank recreational diver, then I see the merit in Odyssey - you'll get in more dives over a shorter period of time, it's really easy, luxury type experience and it's all cost inclusive. Truk Master - not a chance, it's a bucket, nothing like the pics. Thorfinn- you couldn't pay me.
Personally, I thought land based was much more flexible than a LOB for what I wanted (I was diving back mount doubles)- with different interests, skill levels, with longer possible run times as others have said. It also meant that we had any given wreck to ourselves (small boat of six, plus guide), rather than how many from a LOB at once? For as long as we wanted. Totally free to follow the guide, do our own thing or a combination of both.
Cost - I'm don't think there's a big difference, who cares when you're going this far and it's costing as much as it does anyway. Odyssey isn't necessarily a lot more expensive because at BLG you need to factor in meals and nitrox which add up quickly (and they charge hire for manifolds and tank bands for twins). But highly doubtful I would have got in as much diving in as I did. Both LOB you'll be need to book a year in advance, so that doesn't answer the OP question for Dec.
Don't agree with your accommodation assessment. Sounds like your experience was probably pre-Covid, during which they renovated. Everything @Tracy said, agree spot on. Rooms were clean and comfortable, good size, good aircon (a couple did have an issue, I think that was an exception rather than the rule) - although no hot water. Wi-fi in room was slow but worked for internet (but not streaming or photo upload type activites). Food - fine.
To answer the OP on the best dive sites? Too many to list. You will not be disappointed, brilliant.
I'd make the same decision again - land based, Blue Lagoon. I'll be back.