I've worked in a bank for the past six years and feel like I've reached my ceiling given my skills and knowledge and place I work at. What's the best online MBA in the UK for Finance? Is it Warwick? Is an online MBA at a great school less regarded than an in-person MBA at an decent school?

An online MSc in finance from a top school (like Bayes or Alliance Manchester) or the CFA charter, may be a better investment than an online MBA, depending on your target role.  Warwick is certainly the top UK school with an online MBA. 

An online MBA is, yes, generally less well regarded than an on-campus MBA.