Cash vs. 20% seller financing... How do you deal?!?

[Johann Kleisch]

I found a 9 unit that the owner is asking 199k but said it is definitely negotiable.  The owner is also open to taking a 20% second mortgage back.

I told her I plan to write two offers, one for all cash and one with a 20% second mortgage.

My question is what do you suggest I offer for each?  Based on the income, location, and condition of the property I think it's work 199k, but also want to get the best deal possible (and the owner even said she understands I'm looking to get a good deal). 

I was thinking 150k all cash or 180k with a 20% seller second at 10% interest.

Any and all suggestions are greatly appreciated and I thank you in advance!