Whether you're a beginner or experienced miner, the S19 machine is hard to beat. There are several variants (the S19, S19J, S19 Pro, and S19J Pro) which range in hash rate from 90T to 110T, and which one you choose comes down to the upfront cost and electricity consumed.
The S19 is similar in size and shape to prior generation Antminer machines (namely, the S17), but it produces significantly more hash rate. The quality is far higher as well. If you're choosing between an S17 variant and an S19 variant, spend the extra money and buy an S19. You will not be disappointed.
As far as whether to buy the S19j (90TH), S19 (95TH), S19j Pro (100TH), or S19 Pro (110TH) variant, they’re all going to be great machines. Determining which to buy comes down to your budget, availability on the market, and your time preference regarding payback period. If you’re in it for the long haul, buy the most expensive one you can afford. The S19J Pro should catch your eye as it uses the least electricity (3050W), but the S19 Pro will pack more hashing power in the same physical space.
The taller-than-wide shape means you'll get fewer machines per square foot, relative to the Whatsminers M30/M20 series, but hash-for-hash the Antminer S19 uses less electricity, which is a huge advantage when considering your cost per kWh.
The dual-C13 plug design feels odd after you've used Whatsminer's single-C19, but splitter cables are easy to come by, and at 3000 - 3250 Watts, these machines will save you a bit on the electricity bill over the Whatsminer machines.
If I were going to only run one or two machines, this is the machine I would choose.