I do not think that there is a "best method for the isolation of bacteria from soil. That will highly depend on your objectives since you may be interested in isolating either the vegetative or the sporulating soil bacteria.
prepare a serial dilution of the soil sample.if you are interested with the sporulating bacteria,heat shock the solution at 80 degrees for15 minutes to kill the vegetative bacteria.This is the simplest technique that enriches for aerobic spore formers is to pasteurize a diluted soil sample at 80 degrees for 15 minutes, then plate onto nutrient agar and incubate at 37 degrees for 24 hours up to several days. The plates are examined after 24 hours for typical colonies identified as catalase-positive, Gram-positive, endospore-forming rods. Although many species contain sporangia and free spores within 24 hours, some cultures must be incubated 5-7 days before mature sporangia, and the size and shape of the endospore contained therein, can be observed.
We have counts of 10 to the sixth, 10 to the seventh and 10 to the eight with serial dilutions and plating in casein agar (actinomycetes ) and nutrient agar ( agar) further info you can see in the document that we published (https://www.researchgate.net/publication/272565285_INFLUENCIA_DEL_RIEGO_EN_LA_DINMICA_POBLACIONAL_DE_GRUPOS_FUNCIONALES_DE_MICROORGANISMOS_ASOCIADOS_A_LA_RIZSFERA_DE_PALMA_ACEITERA_%28ELAEIS_GUINEENSIS_JACQ%29?ev=prf_pub)
Christoph C. Tebbe
Thünen Federal Research Center for Rural Areas, Forestry and Fisheries
Vivekananda Mahavidyalaya, Haripal, Hooghly
Muséum National d'Histoire Naturelle
National Centre For Cell Science, Pune
University of Nebraska at Lincoln
Seif Ben Tekaya
Texas State University
Brandenburgische Technische Universität Cottbus-Senftenberg
Muhammad Zulqurnain Haider
Government College University Faisalabad, Pakistan
Carlos Bolaños Carriel