I'd be up for playing a modified 'ideal' map, as well as discussing the theory behind it.
Coastal allows for cargo ships for higher internal food and late-game higher gold yield. However, some coastal locations offset this with fewer good tiles (i.e. tiles that yield more than just 2 food, post-Lighthouse). Ideal coastal cities would have minimal 2f tiles, so either lots of water resources and/or lots of decent land tiles.
Benefits of the Great Plains map include:
1) the proximity to other civs, for worker steals and caravan plundering, as well as the possibility of caravans being sent your way after you make peace (limited caravan range early game)
2) proximity of city states for some early gold, at least 1 more worker steal, and a few barb camp missions or worker extractions
3) proximity of civs leads to early boosts to science. I find since playing primarily GP maps that early teching is very easy and the Babylonian GS really isn't necessary (if anything, it tricks me into attempting to build Hanging Gardens and/or Petra, and then getting burned on that!)
4) knowing the general layout of the map from T0 and being able to move and settle with this pseudo previous map knowledge
The very best GP maps offer the above AND also provides enough room for 5+ good cities. Not every city needs to be huge, but you want to approach 20 pop in your smallest city. I think this balance of proximity to AI/CS but enough room to expand would be a tricky part of finding the ideal pangaea map, where it's more likely you'll have room to expand but worker steals and gold income are delayed. A great GP map likely has CS and/or mountains acting as a barrier between your territory and the AI, with the edge of the map acting as a barrier on the other side(s): your first 2 expos can act to block things off (especially if Shoshone) and secure territory so to speak, and then further builds fill in behind.
Sadly, I recently messed up a game where I went 6-city (all mountain) NC with Shoshone and got Scholasticism before Renaissance. The key failing was that I didn't steal nearly enough workers early game. In my best games, I'm getting 6+ workers pretty quickly from the 2 closest AI and a CS, and getting them all back and working promptly.
A downside of GP maps are the lack of jungle, which ideally would be in the 3rd ring (or a bit in the 2nd ring) of your city.
In deciding whether to continue maps or re-roll, I've started putting more emphasis on # of Granary and Stable resources available. Along with luxuries (unique + copies), this should be a key element of putting together an ideal map, though coastal cities would also factor in sea resources. As an example:
Great Plains - resources
*riverside hill next to mountain for capital. Several forest to chop out settlers and early buildings is a nice bonus.
*while riverside hill/mountain is ideal, you can still have an excellent game with just 1 of hill or river for the expos, with most next to mountains (sometimes a non-mountain expo can pick up 2 unique luxuries and a bunch of stable resources inc. horses and is likely worth settling)
*2+ stable resources for most cities, preferably 3+ for capital
*2+ granary resources for most cities, preferably 3+ for capital
*1 unique luxury per city average, with 1 or more extra copies or wonders that give happiness per city average, i.e. 5-city empire with 5 unique luxuries and 4 extra copies and a natural wonder that gives 2-3 happiness. Mining luxuries preferable near capital: these can be connected quickly and sold in peace deals and these tiles are great to work while pumping out settlers.
*circus resources for most cities
Pangaea/Coastal
*would help with Luxury variety
*less emphasis on granary resources, as +food sea resources come into play. Note there is a trade off here with the requirement to tech Sailing/Optics earlier than on GP building the Lighthouse isn't bad but building the work boats takes a lot of hammers.
I think for a pangaea/coastal map to surpass GP, it would need strong food/production land tiles (wheat on plains, salt) to get things rolling and account for the extra hammers required for lighthouse, work boats, and cargo ships (more hammers than caravans). Course, we're talking about the best maps possible, so of course it would have these things
