It just depends what you are wanting to kill,Redwine..in the garden,on a patio or paving..or a single plant which is difficult to dig out..We can help you more,if you are more specific please,as some need a different type of weedkiller..

For me the best weedkiller is a small trowel....chemicals of any kind don´t come into my garden....weeds attract insects...the weed killer will also kill the insects...and as you know we need insects of all kinds for polination...just my opinion...no doubt others will tell me wrong, but I have no problem with that.

True but not always possible if you have a big area to deal with. On lawns Weedol is recommended.Glyphosate deals with anything it touches by absorption through the leaves and is supposed to leave no soil residue. (Use the pure glypohosate rather than brand name mixtures though) SBK for deep rooted stuff. Salt will kill individual dandelions. Were you looking for a more comp0licated answer? I think these are what most of us would use.

I've just used Resolva 24hr for the little bits coming up between paving slabs. Took a bit longer than 24 hrs to kill the dandelions but only needed one spray. Some of the annuals were definitely deceased by 2nd day.

is that a systemic?

Yep - glyphosate based. I was swayed by the TV advert and that it was on offer in B&Q. I don't know whether it's any more effective than other brands but it did the job.