The probable cluster radioactivity (CR) of $^{294}118$, $^{296}120$, and $^{298}122$ is studied by using the unified description (UD) formula, universal (UNIV) curve, Horoi formula, and universal decay law (UDL). The predictions by the former three models suggest that the probable emitted clusters are lighter nuclei, and the calculations within the UDL formula give a different prediction: that both the lighter clusters and heavier ones can be emitted from the parent nuclei. A further study on the competition between $\ensuremath{\alpha}$ decay and CR of $Z\phantom{\rule{4pt}{0ex}}=\phantom{\rule{4pt}{0ex}}104--124$ isotopes is performed. The former three models predict that $\ensuremath{\alpha}$ decay is the dominant decay mode, but the UDL formula suggests that CR dominates over $\ensuremath{\alpha}$ decay for $Z\phantom{\rule{4pt}{0ex}}\ensuremath{\ge}\phantom{\rule{4pt}{0ex}}118$ nuclei and the isotopes of $^{292\text{--}296,308\text{--}318}118$, $^{284\text{--}304,308\text{--}324}120,$ and $^{316\text{--}322}122$ are the most likely candidates as the cluster emitters. Because the former three formulas are just preformation models, the lighter cluster emissions can be described. However, the UDL formula can predict the lighter and heavier CR owing to the inclusion of the preformation and fissionlike mechanisms. Finally, it is found that the shortest CR half-lives are always obtained when the daughter nuclei are around the double magic $^{208}\mathrm{Pb}$ within the UDL formula, which indicates that shell effect has an important influence on CR.