Depends what you want it for, general purpose systemic herbicide ( kills from the root up so no coming back), you wont get better than Roundup, and it's pretty safe as well ( unless your a weed), anything with bark on or woody type eg. brables or heathers, Garlon, does exactly what it says on the tin. Theres probably loads on here that'll give you more brands because they use them on a day to day basis, but I have found these to be effective for the purpose.
Hope this helps
B