I might have a unique perspective on this for you: I'm American, my ex-wife was Canadian (I did all the paperwork for her to immigrate to US), and my fiance is British (I'm researching paperwork fre me to immigrate to UK). A lot of my knowledge of US immigration is old (personal experience from 1996 to 2001), so you might want updated information; my UK knowledge is from research; I haven't applied yet.
Others can direct you better on a spousal visa; I did the fiance visa before and am doing it again, mostly because the timing is quicker (at least for US, where time is very slow compared to UK), and it seemed easier than finding a place to get married first (the traveling fiance would need a marriage visa - one that allows you to travel, get married, and you have to leave - kind of like a tourist visa).
(I saw how huge the USA immigration paragraph was, and haven't even written the UK one, so I came back up here to write a summary: Him to USA takes about 6 months but no fixed amount of salary/savings; you to UK takes only 1-3 weeks but has strict financial minimum requirements.)
For him to come to USA, you would need to file form I-129F (F=fiance), biographical information (a form asking about where he was born, where his parents were born, etc), and an affidavit of support (used to be a pinky-swear that you'll cover his expenses, now it's a 10-year legally-binding contract between you and the US government saying he won't take any public funds, and if he does, they can come after you for the money - even if you were to split up after 5 years, if he stays in America, you're financially responsible for him for another 5.) On the plus side, from what I remember, you do't need a specific amount of money, just enough proof of employment that you can support both of you.
About a month later, he would then receive a letter in UK sending him on a scavenger hunt (passport, passport photos, chest X-ray (tuberculosis) was required in 1996, and he sends it in to London).......about another 4 months later, he'll get a letter out of nowhere saying to show up in London next week (so make sure his employer knows he'll need a day off with little notice someday). He then shows up, waits around various rooms in the American consulate all day, gets questioned in a teeny room (if you come in with him it's a shoe-in, the agent was shocked that I came to be with my fiance, and that was just a drive from New Jersey to Montreal, Canada!); he then gets a visa stuck in his passport giving him 4 months to enter the US. (When he does, make sure to ask for employment authorization to be stamped on his I-94 card, otherwise he can't work until he gets his conditional permanent resident card!) Once he enters the US, you have to get married and file for change of status to conditional permanent resident within 90 days(!); he can't leave the US from when he enters until after getting his conditional permanent resident card in the mail, which takes a few more months.
For you to move to the UK, you first collect a lot of proof that you're a real couple (Skype logs, boarding passes, pictures, and any paid wedding plans like renting a hall, flowers, etc; I read that an engagement ring receipt doesn't count, but others on the forum says it does, so stick that in anyway). You file online for a fiance visa, which only takes 1-3 weeks! for approval, and you can even pay extra to get it expedited and have it in 3-5 DAYS!!!! (People dealing with only UK immigration might wonder why that makes me so happy; it's because going from UK to USA takes 5 MONTHS just for the interview to get approval, and there's no option to pay an expedite fee for a fiance visa.) (The timing of the next sentence might be wrong, I forget the exact order): Before your interview, you have to go to a US(?!) Application Support Center to get fingerprinted, and you have to mail everything (including your passport!) to the UK consulate in New York City (there may or may not be one closer to you). You get approved just by the stuff you mail in, no interview, so make sure you send everything. You have to send TWO of everything (original and copy); they keep the copies & mail back the originals.
As for timing of the wedding, the good news is you get 6 months to get married and file for change of status, not 3 months like USA; the bad news is unlike USA where you have up to 4 months to enter before starting the clock for the 90-day filing deadline, your 6 months start the day they approve you and put your visa in the passport (not when you enter the UK, not even the day you receive the passport & visa). But overall, UK is the better deal: Instead of waiting about 5 months for approval (not knowing what week or month that will be) and then getting 4 months to enter and 3 months to get married and refile, you get your approval within weeks of your initial application and then get 6 months to enter, get married & refile.
The hard part with the UK visa is the financial requirement, depending on your savings and his salary: He needs a job (you don't count because you're not allowed to work in UK yet) with a salary of at least £18,600 (about $31,000 based on a £1 = $1.67 exchange rate, better to guess high) for at least 6 months, and he, you, or both of you combined need a minimum of £16,000 (about $27,000) savings in bank accounts in just your names (either of you) for at least 6 months prior to applying. If he doesn't make £18,600, then for every £1 less, you can have an extra £2.50 in savings (since your next interview after all this is in 2 1/2 years, they figure you can live off the savings for 2 1/2 years). Therefore, even with no proof of employment, you can qualify if both of you combined have £62,500 (about $105,000!) in the bank for 6 months (or immediately if you sell a house you owned for at least 6 months and have $105,000 in the bank after the sale). (In 2 1/2 years when you have to renew, they'll check the same financial requirements, but that time, your salary counts.)
The other hard part of the UK visa is the proof of a intent to marry: Although Skype logs, flights and photos will prove you're in a genuine relationship, they want proof that you're going to get married within 6 months. It's hard to plan a wedding when you don't know when exactly you'll be there (or if you're still in America), but at least knowing you should get approved within a month of filing, you have a rough date of when you can enter, so it's easier to pick a wedding date.
(I'm sorry if this is way too much information, but hopefully you or others will find it useful, if they can find it way down here in page 3 or 4 of this thread. For more info on UK fiance visa, go to www-dot-ukba-dot-homeoffice-dot-gov-dot-uk/visas-immigration/partners-families/citizens-settled/fiancee-proposed-cp (sorry; new users can't embed hyperlinks).)