i like and use both of them - MetaBall and WaterMorph, but..
as for me, problem consist in the way of 3d model's creation for this modules. i have a light experience in assembling of 3d objects - in software environment and only with my own hands..
anyway, i can see it, and easy modify it. coordinates of the nodes of WaterMorph's models must be generated beforehand with any file-writing application, even in quickbasic but i can't see the model before i run R4 and press lovely "reload" button. and those shapes appears too much organic and very low detailed..
much better to create the models with MetaBall, (i was posted my experimental scene here ). but they have stepped size/radius of the balls, balls can't get out from the cube boundaries and most dramatically - it's impossible to create more than 64 balls - this is very very low amount for creation of detailed model (8x8 grid only..). MetaBall, as for me, perfectly suitable for drawing liquid 3d surfaces with mad sets of trigonometric functions..
gl.modAddTri will be my fav when you unbend it..
but i still scared, how can i create a tiny bit more complicated objects? most inconvenient for me - to specify the order of edges. i think, i should create model in 3d editor, then export it in raw, extract from ascii-file coords of vertices and carry-out it in gl.modAddTri thrice in correct order.. 
probably, there can be more user-friendly way.. i think, this is much more easy to draw model in 3d-editor and then move it vertices in new position (and see result on the screen) for creation of next morph phase. and i will be able to create sequence of 3ds models (one object deformed in different ways) and load it together one after another like watermorph objects..
or, if it will be possible (this the very best way, imho) to get acces to coordinates of each loaded vertex of 3ds object by it number (like in MetaBall, numbers of vertices can be easily finded in major 3d editors - simply turn-on displaying of the numbers (3ds max have this option)). this way will be much more effective! in this way i may not think about order of edges, module will operate with edges's orders from 3ds file!
maybe other, lowpoligonal editors can display, does anybody know about it?