Since you are looking for Discount brokers, in my experience of 3 years full-time trading, you cannot rely on any of them for consistent results. There are pros and cons when it comes to their platforms. Fyers have good scanners however, they are not yet volume tested and their platforms are very resource hungry. Upstox emerged as a good contestant but their web based platform have consistently deteriorated. More or less everybody provides the same set of price based indicators. Some brokers like TSO or Finvasia have further reduced their brokerages but you won't get anything extraordinary in terms of their platforms. Anyways, if you go with FoxTrader provided as a partnered platform by these brokers (barring Z) you will have access to some meaningful stuff. Caveat is that FoxTrader comes with a hefty subscription cost.
Platform wise TradeTiger still outshines in comparison to the platforms provided by all these discount brokers. But SharKhan charges a lot especially if you want to play the markets using Options.
At this juncture you will have to figure out what exactly you need and your game plan to trade the markets instead of relying on what is being provided to you. More importantly you will need to determine your time-frame. For me day-trading did not work, and in my early days I soon realized that I am only making my broker rich everyday by using their platforms.
Now how do you know what works for you? Unless you make your own strategies and backtest them, there is no way. I can only share my story, I downloaded AmiBroker's User Guide and on their 30 day trial version experimented all that I could, then got their license by paying a one-time fee. You will have to read TA books (most of them are freely available on the internet) and strategize your own plan. It takes time, extremely difficult and not everybody's cup-of-tea. For first 6-9 months, it will be very hard but then you get to enjoy your perseverance for sure. The reason I love Amibroker is that you can built anything that you want, you no longer need to rely on anybody (Foxtrader, TradeTiger sab bachey hain iske agey). Although you get free AFLs scattered across the internet, but IMHO copy-pasting does not work. So, yeah, lot of work needs to be done.
Now going back to your query, apart from Z, I have not experienced drastic OMS failures in any other brokerages. Occasional glitches have occurred but not to the extent of losing money, the way it happens with Z.
Another option would be Interactive Brokers. Even if, they have reduced their prices but they are not a Discount broker.
So, choose wisely. All the best!