Ed will tell you to avoid chromexcel, and it does mark and scuff easier than most other leathers to be honest. I have oxfords in chromexcel and SDs in dress, of the two I would go for dress leather as it is much harder wearing and evolves beautifully.
The exotic leathers are really a matter of your personal taste, but be warned that water buffalo is very thin and can split.
A double midsole will obviously give you a little more height, but can look a little "clunky". A leather sole is very popular, but can be not practical if you live somewhere wet, like me. I favour a vibram half sole, and a single leather midsole for versatility.
Style of boot is entirely down to personal preference, along with colour etc....