B.tech is bachelor of technology. it mainly deals with technology field. if you are strong in mathematics and physics then you may choose it as your career option. you have to study totally based on technology.
B.Arch is bachelor of Architecture. it is also related to technology but mainly it deals with designing part of architecture. to become a good architecture you must be a good designer. if you like physics mathematics as well as designing then go for architecture. if you become a very good architect then scope and opportunity and scope will be very high for you.
now you have to decide in which field you have more interest and in which way you want to go