To add to this, the UK embassy has a website with as good information as anywhere regarding DCF in London. It's already linked above, but worth repeating.
Each USCIS field office is different and some procedures tend to be country specific. For example, London USCIS does not require any evidence of bona fide marriage with the I130 when DCFing, only at the interview. This is the only instance I know of where bona fide marriage evidence is not submitted with the initial petition. OP should use the embassy website as the definitive guide to DCFing in the UK.
K3 is actually obsolete now. Typically people will use the DCF route if they qualify or very usually the IR1/CR1. The former is quicker than the later, provided you meet the qualification. The only thing I would point out to you, as you should be aware that the UK immigration system (which you are in part of the process already) can take a while with the steps of the process and also be quite expensive - however, I would usually encourage the couple to stick with it if they've started, as it will grant better options in the future. Having dual citizenship gives you an easy way to choose whichever country you want to live in with your husband for the long term with no questions, during a potentially upcoming uncertain time for the UK.
Let us say for instance you move back to America, but decide later on the UK is calling you back for whatever reason (it happens, I've seen it happen). You'd have to start from scratch all over again, and spend a lengthy amount of time apart, as the UKC would have to return to the UK without you and raise the qualifying work/money requirements to bring you back. The UKC moving back to the UK would also complicate their own immigration process in the US. What I'm saying is, if you're sure, absolutely sure, be prepared to stick with one side of the process for the long haul and see it all the way through until citizenship.
Whatever option you decide to go with, check out the guides section of this website, it'll tell you a lot of what you want to know.
Best option is DCF (Direct Consular Filing) through the London Embassy. You'll file an I-130 there (as opposed to sending it to USCIS in the US) and your husband will eventually end up with an IR-1.
This takes a few months (as opposed to 12-15 months if filed through USCIS in the US).
NinaRenae reacted to Jorge V in New to all this and looking for help