Tough call.
I did Blinn for a year and transferred into A&M. But when I applied for fall 2003 I was given the early transfer program as an option. Basically had to go to any public school in Texas for a year and get a 3.0 and then I could pretty much transfer in automatically. I don't think this is offered anymore.
I really enjoyed my time at Blinn and took classes from a couple of the best profs I had in college. The class sizes are small and the profs are actually teachers and not there for research. Most of the profs spent some time at A&M as well. Biggest pro is that you're in College Station. But you really have to stay motivated because as you mentioned it is not a slam dunk these days transferring in from Blinn. My year at Blinn was probably one of my toughest because of the pressure to perform to get into A&M. A lot of people go to Blinn and never make it to A&M because they forget the reason they are there. Some of the classes were actually harder than the same classes my future wife at the time was taking at A&M. But because the caliber of students wasn't as great as A&M it was easier to do well in classes that curved their grades. Everything ended up well for me, I went on to graduate with a degree in Electrical Engineering and took a really good job out of school. Two of the guys I studied with in my calculus classes at Blinn went on to get degrees in Civil Engineering and actually ended up at the same company as me. While I wouldn't have originally picked it, I'm proud of the path I took. In some ways I think it helped me stay focused on school when maybe I wouldn't have taken it as seriously as if I started at A&M.
Now my sister who is getting her Aggie ring today decided to go to the TAMUG route. SHE LOVED IT THERE. Almost too much. She actually spent 2 years in Galveston, not because she had to, but because she wanted to! If they had a major that really fit her she would have graduated from Galveston. She was trying to fit herself into the curriculum at Galveston finding any reason to stay.
Finally, my sister conceded that it was the best for her personally to transfer to College Station. I can tell you that TAMUG students are as redass as they come, much more so than I ever was. They get great football tickets and carpool to the games in College Station. They follow most of the same traditions with a few of their own mixed in. They have a really nice new on campus dorm. I'd recommend living on campus, my sister still keeps in touch with all of her Galveston friends that she met living on campus. I'll admit its not the nicest campus, but there's a pride there with the students that it is their campus. Knowing what I know now, I'd probably go the TAMUG route as it is the safer bet and you're already a TAMU student.
Being in college station and trying to fit in with people that go to A&M while at Blinn can be difficult. There's a bit of stigma to overcome and sometime you're looked down upon. But that just made me work harder. Its hard to make long lasting friends with people at Blinn because you may be on a different path, and its harder to make friends at A&M because you didn't get that on campus bonding. Transferring in you feel like an outsider who doesn't know what to do at football games. Nothing that can't be overcome though. If you do decide to go to Blinn I'd recommend living in a private off-campus dorm near A&M. I stayed at the Tradition in Northgate. That way you'll be exposed to new people easier.