If you export as .3ds then its all triangles anyway.  lwo has issues in poser misinterpreting n-gons. 

The best format in my opinion is obj which c4d should have as an option. 

You could look at transposer and see if thats a good option for you .

Those sort of triangles on the flat wall may be a smoothing issue in Poser. You can try unchecking smoothing in object properties, try changing the crease angle or unweld / split vertices in the modelling program .

http://www.sharecg.com/v/22750/Text-Entry-Tutorial/modelling-for-Poser

the link is a document I did on modelling for Poser , showing some of the problems and solutions . Its not perfect and was written for Poser 5 but you might find it worthwhile .