If you don't get at least Bs at GCSE you will seriously struggle at a-level. Looking at your results, btec would probably be best, but if the results are due to lack of motivation/revision, then perhaps consider a-level, especially if you think you can do better.
You can always apply for both a-level and btec, then when you get your results you can go for whichever. Some colleges don't let you take a-level unless you get a C/B at GCSE, so you should probably be aware of this.