What antenna is equal to it's performance in today's market?
I personally don't know of any comparable antenna to the Channel Master 5094/5094A Monitenna that is currently being manufactured and sold today. The Antennacraft ST2 Scantenna along with the Radio Shack equivalents (Radio Shack catalog numbers 20-042 and 20-044) were of a very similar design to the Channel Master antenna but all of those antennas have also been discontinued and are no longer in production. Some sources for these antennas today (used and sometimes even new-in-box) may include eBay, Craigslist, estate sales, ham swap meets, RR classifieds, etc.
As a point of interest I previously contacted Channel Master about bringing back their 5094A 5-band Monitenna seeing that there was a market (in my opinion) for a reasonably-priced all-band scanner antenna that had very good performance. They did reply and stated that they had no interest in manufacturing/selling a scanner antenna at that time when I contacted them.