That's a really tough situation. There is no right answer, and it's all gonna depend on a few things and your appetite for risk.
First off I wouldn't take any action without seeing if you can do both. Is there a summer scheme instead of spring, you may still be able to switch to that, and you may be able to take annual leave or unpaid leave then, or if you decide not to do the scheme, maybe they could offer you a direct TC AC. Alternatively ask if you can delay the start of the grad scheme until after the scheme. If none of those are options, then ultimately it's down to you. How much do you want to be a solicitor? What would you do instead of this grad scheme if you don't get the TC? Have you had much luck with other vac schemes/is this your first cycle applying? How much are you in need of full time work right now?
The fact you got this vac scheme, means you are good enough and you could definitely get future ones. But there is always luck in the process and it very possibly could take you several more cycles to get anything again, which is also made harder by being in full time work. Not to say that getting a grad scheme is not hard, because it certainly is, but I would argue it would be much easier to find another full time office job, than to get another vac scheme. Personally I would do the vac scheme, even if it meant giving up the grad scheme, but again that's from my perspective where I don't really need full time work at the moment, I'm also graduating this year so I'm maybe not quite as keen to get into a career as someone who's been out of uni for a few years. Also for me personally, I don't have much interest in HR, so it is a clearer choice for me.
Either way, you're landing a good role/good experience, both of which will help you in the future.
