I think the two witnesses in Revelation are the two churches in Rev. Chapter 1 that pleased G-D. What do you think? Granted I'm in the minority on this one but I really believe it.
The passage about the two witnesses begins with Revelation 11:3-4. "And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth. These are the two olive trees, and the two candlesticks standing before the God of the earth." Compare with this a passage in Zechariah 4. Zechariah saw a menorah whose oil was coming directly from olive trees on either side of it. "And I answered again, and said unto him, What be these two olive branches which through the two golden pipes empty the golden oil out of themselves? And he answered me and said, Knowest thou not what these be? And I said, No, my lord. Then said he, These are the two anointed ones, that stand by the Lord of the whole earth." (Zechariah 4:12-14) If we can figure out the meaning of the passage in Zechariah, we should be able to understand the one in Revelation.
Two people are mentioned in the context of the passage about the olive trees and menorah. They are Joshua the priest (not to be confused with the Joshua who took over for Moses) and Zerubbabel the prince. Interestingly, both of these men would have been anointed, being a priest and the heir to the kingdom. Zechariah 3 also mentions a "branch," which appears to be a prophecy about Messiah (which means the anointed one). For those of us who believe that Jesus is Messiah, this prophecy would be about him. Jesus was born in the lineage of David and Zerubbabel, and so has that anointing as king. The writer of Hebrews points out (chapters 6-9) that Jesus is a high priest, and so has the anointing as priest. This might indicate, then, that the two witnesses of Revelation are the priesthood and kingship.
The chances of it referring to Jesus are slim, though, because the passage says the witnesses will lie in the streets of Jerusalem for a time. Of course, that would also mean that it would not be likely to refer to the two cities you mention. On the other hand, it is all symbolic. So the concepts of kingship and priesthood could die after the destruction of Jerusalem in 70 AD, and that would fit this passage.
In researching this I consulted one commentary that claimed that the witnesses were the Old and New Testaments. While these certainly both witness to Jesus as Christ, I don't think they are the two witnesses of this passage.
In the end, I don't know who the witnesses are. They are not likely to be cities or churches because of the passage about lying in the streets of Jerusalem. They are likely related in some way to the anointed ones of Zechariah 4, but in what way is no longer clear to us. Many of the symbols in the Revelation were clear to the people to whom it was written, but their meaning has been lost in the time since the prophecy was fulfilled.