\documentclass{article}
\usepackage{tabularx,tabulary,longtable,dcolumn,siunitx}
\begin{document}

Standard LaTeX tabular:
\begin{tabular}[t]{llll}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular}

LaTeX tabular with *-operator:
\begin{tabular}[t]{*{3}{l}r}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular}

\begin{tabular}{*{3}{l}>{\tiny\hfill}l<{\hfill}}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular}

\begin{tabular}[t]{*{3}{lc}r}
  1 & 2 & 3 & 4 & 5 & 6 & LaTeX-insert-item \\
    &&&&&&
\end{tabular}

\begin{tabular}[t]{*{3}{lc*{2}{l}} r}
  1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & LaTeX-insert-item \\
    &&&&&&&&&&&&
\end{tabular}

Standard LaTeX tabular*:
\begin{tabular*}{1.0\linewidth}[t]{@{}lllr@{}}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular*}

\begin{tabular*}{1.0\linewidth}[t]{@{}*{3}{|l}|r|}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular*}

tabularx:
\begin{tabularx}{1.0\linewidth}{llX}
  1 & 2 & LaTeX-insert-item \\
    &&
\end{tabularx}

\begin{tabularx}{1.0\linewidth}[t]{@{}>{\tiny\hfill}l<{\hfill}lX@{}}
  1 & 2 & LaTeX-insert-item \\
    &&
\end{tabularx}

\begin{tabularx}{1.0\linewidth}[t]{*{3}{|>{\tiny\hfill}X<{\hfill}}l}
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabularx}

longtable:
\begin{longtable}[l]{llr}
  \caption{Some caption}\\
  1 & 2 & LaTeX-insert-item \\
    &&
\end{longtable}

\begin{longtable}[c]{*{3}{l}r}
  \caption{Some caption}\\
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{longtable}

\begin{longtable}[r]{*{3}{lc*{2}{l}} r}
  \caption{Some caption}\\
  1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & LaTeX-insert-item \\
    &&&&&&&&&&&&
\end{longtable}

dcolumn:
\begin{tabular}{D{,}{,}{2}D{,}{,}{2}D{,}{,}{2}}
  1 & 2 & LaTeX-insert-item \\
    &&
\end{tabular}

\begin{tabular}{*{3}{D{,}{,}{2}}}
  1 & 2 & LaTeX-insert-item \\
    &&
\end{tabular}

siunitx:
\begin{tabular}{%
  s
  S[table-number-alignment = center]
  s[table-number-alignment = left]
  S[table-number-alignment = right]
  }
  1 & 2 & 3 & LaTeX-insert-item \\
    &&&
\end{tabular}

\end{document}