Perella or Citi FT IBD London

Citi - no doubt about that.

1. One of the biggest banks globally, and top ranking IBD
2. Very large institution with longer history and higher deal flow so more opportunity for professional growth
3. More opportunity to move around between functions and also geographically (if you don't plan to stay in London for long), also if you want to try out a different function such as Industry groups / M&A / ECM or DCM - probably better graduate programs too and training
4. 2016 ranked #5 on Dealogic on Global M&A advisory (also top 5 on financings)
5. 2017 YTD ranked #6 globally on M&A advisory
6. Probably can build a good network at Citi with all the functions and people you meet working there or yo end up advising

I am sure there are many good things about Perella, but I would go the Citi route, and if you don't like the job there, I don't see it being too difficult to make a switch down the road - and I get that you're worried about the brand but I think you could easily leverage the Citi brand to get into a Megafund given its ranks/reputation etc. (just my guess - I am no expert by any means man).

Hope that helps.