For molecular diversity studies there are several softwares available...suchas TREECON, Phylip, MEGA, DAMBE etc. and all of these are available free of cost ......see if these are useful for the kind of studies you are planninf
I think MEGA 4 verison is good once, becoz, color difference should be made in your tree, my advice firstly, your all respective genome was aligned by using Clustal X software after that you can using the Mega 4 version
First of all Congrats to you, My opinion for MEGA -4 and 5. The MEGA software is free version. If make construction for phylogenitic tree before your all sequences was alingned with help of Clustal X after you can use this software,.
I find Mega4 is easily accessible and appropriate for use since it has colour features that can be used to indicate specific known phenotypic traits associated with the genotypes of plant/animal/microbe as clustered in the dendrogram..