The answer to your question is that it will depend on several factors. Perhaps most importantly what plants you want to build the phylogeny for. The DNA markers that you wanted to build a family-level phylogeny are different from those that you would if you wanted to study relationships within a genus. If you could explain what the broad goal is it would be easier to suggest candidate markers.
Thanks Mr. Winkworth sir, I actually wanted to study the evolutionary relationship of grass plants with others plants.In that case to make a phylogeny which markers are preferable?
if you want to receive answer for your question you may clarify many aspects of your investigation. Most important of them:
What level of phylogeny you want to study (species, subspecies or maybe higher livels)
Grass plants is also very wide notion. What volume of species do you plain to study? Is there hybrids, apomictics, interspecific crosses? What outgroup you plain to use?
What the main aim of your work and phylogenetic reconstruction?
All of these questions directly connected with what markers to choose in your study.
We have great wariety of markers because the can be used for acievement the very different aims, but all this aims can be located in phylogeny. Phylogeny in general is very wide definition too.