On way would be to define \hcoices (or \vchoices) using a \foreach form the pgffor package.
1. Using exam class:
The first part below if using the choices environment, the next two are the custom ones that you would use:

Notes:
- You had a minor typo in your code which I have corrected below.
\end parts should have been be \end{parts}.
- You should also be using the
choices instead of parts environment for multiple choice options.
Code:
\documentclass{exam}
\usepackage{pgffor}
\newcommand{\hchoices}[1]{%
\par
\begin{oneparchoices}
\foreach \Choice in {#1} {%
\choice \Choice
}%
\end{oneparchoices}
}%
\newcommand{\vchoices}[1]{%
\begin{choices}
\foreach \Choice in {#1} {%
\choice \Choice
}%
\end{choices}
}%
\begin{document}
\noindent\textbf{Choices:}
\begin{questions}
\question Which among the following focuses on values?
\begin{choices}
\choice Axiology
\choice Epistomology
\choice Philosophy
\end{choices}
\end{questions}
\hrule\medskip\noindent\textbf{hchoices:}
\begin{questions}
\question Which among the following focuses on values?
\hchoices{Axiology, Epistomology, Philosophy}
\end{questions}
\hrule\medskip\noindent\textbf{vchoices:}
\begin{questions}
\question Which among the following focuses on values?
\vchoices{Axiology, Epistomology, Philosophy}
\end{questions}
\end{document}
2. Without exam class:
To produce something similar without the exam class, you can use enumerated lists. I used the enumitem package below as it is more flexible:

Notes:
- Thanks to Heiko Oberdiek for the solution to How to create an inline list via a macro which was needed here.
I have used \hspace*{2.0em} to separate the individual horizontal items, but if you prefer that the items be more uniformly distributed based on the number of items, one can use use hfill for the itemjoin option:
\setlist*[MyHChoices]{label=\Alph*., itemjoin={\hfill}}
Code:
\documentclass{article}
\usepackage[inline]{enumitem}
\usepackage{pgffor}
\newlist{MyHChoices}{enumerate*}{2}
\newlist{MyVChoices}{enumerate}{2}
\setlist*[MyHChoices]{label=\Alph*., itemjoin={\hspace*{2.0em}}}
\setlist*[MyVChoices]{label=\Alph*.}
% http://tex.stackexchange.com/questions/78628/how-to-create-an-inline-list-via-a-macro
\newtoks\gInlineToks
\newcommand*{\hchoices}[1]{%
\global\gInlineToks{}%
\foreach \Choice in {#1} {%
\global\gInlineToks\expandafter{%
\the\expandafter\gInlineToks
\expandafter\item\Choice
}%
}%
\par%
\begin{MyHChoices}\the\gInlineToks\end{MyHChoices}%
}%
\newcommand{\vchoices}[1]{%
\begin{MyVChoices}
\foreach \Choice in {#1} {%
\item \Choice
}%
\end{MyVChoices}
}%
\newenvironment{questions}{
\let\question\item
\begin{enumerate}[label=\arabic*.]
}{%
\end{enumerate}
}
\begin{document}
\noindent\textbf{hchoices:}
\begin{questions}
\question Which among the following focuses on values?
\hchoices{Axiology, Epistomology, Philosophy}
\end{questions}
\noindent\textbf{vchoices:}
\begin{questions}
\question Which among the following focuses on values?
\vchoices{Axiology, Epistomology, Philosophy}
\end{questions}
\end{document}