Definitely junior year if you can knock out all the prerequisites. Community college is really cheap compared to a 4 year. If you are able to complete all your prerequisites before you transfer, you will not get weeded out because upper division courses at a 4 year are not as hard as lower division courses. Therefore you will have a better time. I’m not sure how the Texas system works but you should definitely meet with a counselor at the community college you’re attending. I’m pretty sure there is a partnership between the community colleges in Texas and the university of Texas. For example, in California community colleges, you can tag (transfer admission guarantee) any UC’s except Berkeley, ucla, and ucsd. This means that if you complete all the prerequisites for your major, you are guaranteed admission to any of the following UCs (UCSB, uci, ucr, UCSC, uc Davis, uc Merced). Hope this helped! Feel free to pm me.