US citizen currently working in the UK on a T2 ICT long term visa - marriage question

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I am US citizen, currently working in the UK on a T2 ICT long term visa - my girlfriend is from Mexico living in Mexico.

I'm planning to propose on my holiday but wondering what options to consider for eventual return to US.

1. Apply for a UK Marry Visit Visa and marry in the UK - then return to US after my assignment.
2. Request an early return back to the US and apply for a Fiancée Visa when I'm back in the US.

I would like to choose option #1 so we can stay in the UK as long as I can but I have a few questions / concerns.

1. If we chose option #1 above, then we couldn't utilize #2 above when I return back to the US - what options would we have when I return back to US and how long would the process take ?
2. Would it be easier to choose option #2 above and return to US?

Any concerns / other options related or unrelated to the above ? Your advice would be extremely appreciated.

Thanks in advance...