Graduate Accounting --> Big 4 ---> IBD ???

Of the options you've listed, I'll only speak to those that I have experience in (lateraled from Big 4 audit to IB), i.e. have no clue what a Private Banking Analyst does. I would highly suggest you go with the Big 4.

No offense to the poster above me, but I would never choose Mid-Tier accounting firm over Big 4 given the options, even if it was choosing between Valuation at Mid-ter vs Audit in Big 4. In public accounting, there isn't such a thing as "elite" accounting firms, it's BIg 4 and everyone else. You're not going to get the same stamp approval with a McGladry/GT/Moss Adams/etc as you would Big 4, there's a huge discrepancy in perceived quality of firm. I'm not saying you can't do well and have a successful career, but from a pure "prestige" standpoint, that's reality. You can easily transfer to Transaction Services (Transaction Advisory Services at PwC) Valuation group after one year of audit, or into the M&A DD group after 2 or 3 years, assuming you're high ranked. Big 4 alumni place fine into MBA (I've seen M7 all the time either on LinkedIn or from my personal network). The lack of perceived placement into MBA is because most Big 4 alumni don't want to go to MBA. MBA typically leads to IB, PE or consulting. Reality is most Big 4 staff don't even want to work Big 4 hours, let alone IB hours or consulting travel. PE is out of the option for the most part but rarely does someone in Big 4 think about PE to begin with.

The problem with a boutique IB is the lack of recognition (assuming we're talking about a genuine tiny boutique and not a elite boutique or MM firm). If you told me you were dead set on joining IB as an analyst, I would slightly suggest choosing this over Big 4 (yes, slightly). But since your goal is post-MBA IB, then you want the job to best position yourself for IB. It's hard to compete with guys from GS/MS/JPM/Moelis/etc + top PE experience when you come from a boutique M&A shop. I'm sure there are guys that get into good MBAs, but I honestly don't believe you'll be a more qualified MBA candidate coming from boutique banking compared to Big 4. At least in Big 4, you're the best of the best in your field. You'll also develop leadership skills both from auditing and other firm-sponsored activities. Big 4 also does a great job about constantly providing training and mentoring (not always audit related) for its junior staff. I've yet to see any IB firm spends as much time and effort developing their junior employees' overall career.

F500 Corp Fin is highly ambiguous. Are we talking Corp Fin that does mostly corporate development, i.e. in-house M&A? If so, then that's definitely a top choice as well though not the only. If you're talking about a Financial Analyst that does FP&A or accounting related work, I'd pass. You can easily become a Financial Analyst at a FT500 company after a year of Big 4 experience on your resume, but you can't do the reverse. There are small windows of opportunity to pursue certain paths (Big 4, IB, PE, etc). The window to have FT500 on your resume is plenty, whether it's pre-MBA after Big 4, or post-MBA after IB Associate.

Big 4 may not be the "sexiest" job compared to IB, but there are a lot of soft skills you develop that are more important than the technical knowledge you gain as an analyst in IB for post-MBA Associate. You don't need to be extremely technical as an Associate, that's what you have analyst for. What you need is be able to client facing, and manage expectations and execute transactions. Guess what you're doing in Big 4, particularly as the Senior Associate and up level? You're planning the audits and acting as the key connection between the Client, the Senior Managers and Partners, and the Associates below you. That's the same thing as managing expectations and executing a process, but just in the context of an Audit. Also, the Big 4 network tends to be pretty strong. Rarely have I reached out to a Big 4 alumni on Linkedin and not received some kind of response. Especially those that did Big 4 and now are in banking (whether Analyst or Associate), most tend to be pretty helpful because they've been in your shoes.

Anyway that's my semi-long explanations (we can go into more details if you have specific questions).