like one of the other posters said the problem with both hotels is, particulary in the case of the Stratosphere, towards the upper end of the Strip and away from a lot of other places you may want to visit.
So though you may get a cheap rate you may also find that you have extra cost in taxi's etc.. and though I think both are within walking distance of the Monorail it can be a fair walk (we stayed at the Mirage, in the centre of the Strip, and it took us at least 20 minutes to walk from our room to the nearest monorail stop) so you're going to be spending a lot of time travelling. The Strip Trolley does go up to the Stratosphere and past Circus Circus , it's fun but takes an age.
I'd spend more and go for a centrally located hotel where you can walk to attractions