Actually, the hash rate is not so very important if you have units that have a 1-month lifespan, and buying miners in unknown brands will lead to no support so only buy a miner with lots of support.
Sample Antminer or Avalon these miners have lots of support on their website even here on the forum you can find lots of threads and guide about these units.
If you care about efficiency then Antminer s19 pro or their new miner called s19 pro+ hyd running at immersion(water) cooling.
If you still want to get more suggestions from an expert then try to contact this
offordscott he will also help you to choose what is the best option to buy.
If you are looking for an ROI calculator you can check this tool
https://www.mycryptobuddy.com/