To add to gokeeper's post:
I'm dealing with the very same issue as the OP. Wife and I are visiting the falls in November and currently I have reservations at both the Hilton and the ES. Not sure where we will be staying but now we have a choice. The ES is a bit less expensive than the Hilton.
In addition to reading all the reviews of both properties here on FT, I also perused the documentation on TA. I noticed a review from someone who had stayed at the Falls ES recently and had some comments on parking at a nearby casino that I asked about in a PM. That person replied:
"The Casino is a block away. When you arrive at the Embassy they will let you park right outside the entrance door, go inside to check in and carry all of your bags up to your room. After that you can move your car to the Casino lot. We left our car there overnight and when we left the lot the next day we were charged $5.00 at the time of exit. We re-parked later that day and when we left again the following day we were charged another $5.00. $10 bucks total compared to the Embassy charging $20 per day. I didn't find anything un-safe about it. Everything was fine. Have a good time!"
We are also staying for two nights. One reason I PM'ed was because I wanted to know what the person felt about the security of the parking lot. Apparently it was not an issue.
Hope this helps.