Ortho Weed B Gon plus Crabgrass control is a great Step 1 weed killer. It’ll cover a large variety of weeds all at once, and comes in a variety of shapes and sizes.
For small lawns with tons of weeds I like to use the Ready to Spray (RTS) hose end version. Usually lawns less than 5k this is perfect, you attach it to your hose and spray away – you can cover large areas quickly.
For lawns with small amounts of weeds I like the 1 gallon Ready to Spray with the trigger option. No mixing, no mess, just pull it out once a week, walk around the yard and spot spray anything that pops up.
For large lawns with tons of weeds I would recommend the concentrate. It’s a little more work but you can mix it yourself and save some money. It also means you can put it in a backpack sprayer or other sprayer.
The Ortho Weed B Gon brand is a solid solution for killing weeds. There are cheaper generic versions but this having the 2,4-D/Dicamba/Quinclorac combo is a good bet if you just want to grab something readily available that will work on a large variety of weeds.
If you do find a weed that Ortho Weed B Gon Plus Crabgrass Control can’t kill, check out Step 2 on the weed funnel.