NFCU
PenFed
Affinity FCU
NFCU is my main banking institution. The other two I wanted to go ahead and establish relationship with for future financing or credit card options. Shooting for Affinity VS rewards 2023.
Alliant - joined in 2019 as they allowed ITIN and non-residents (I live outside the US) and thought they would be good for savings. I used them as my primary institution for checking and savings between last year and early this year as my previous main bank, Union Bank, announced last year that it is merging with US Bank. I didn't want to have to deal with changing the routing number/account number on the autopay for my cards and Alliant's checking/savings have competitive interest rates, so I switched and opened a checking to go with my existing Alliant savings account. Overall I like them, the savings rate is great and the checking rate is good for a checking account. Phone support was always very good, although online messages always took a day or so longer than they said it would. There were a few cons - the debit card cannot be frozen or locked, only replaced if you lose it. The website is seemingly down for maintenance every few days, and although Alliant participates in the co-op ATM network and refunds fees, it doesn't participate in shared branching.
I used to use Wells Fargo when I was in the US and needed to deposit any leftover cash at the end of my trip, but they recently started requiring US addresses so I had to close my checking with them. Using Alliant would mean I would have to find a deposit-taking ATM which aren't super common and can run into issues.
Penfed - joined in 2019 simply because they allow non-residents and I thought 'why not' 
They have recently introduced free checking, but until recently you had to have a $500 minimum balance. The 'premium online savings' account usually is close to or matches Alliant's rate.
United Nations Federal Credit Union - my current main checking/savings that I switched to when I looked for an alternative to Alliant earlier this year. They are the best option so far for me personally, although my needs are very niche as a non resident! They are totally fine with non-residents, allowing you to fill in a w8 (or w9) form online on online banking, while Alliant and Penfed make you fax, email or mail a copy, and they even have branches in Europe and Africa. They participate in shared branching, and, if you have at least a $2500 minimum balance (in any account with them, it could just be in one account or spread out, as long as you have at least $2500 with UNFCU) , they will refund up to $10 a month in fees (they also refund $25 with 50k balance and $50 with a $250k balance, but I am basing my opinion on the $10 rebate.) This is lower than Alliant's $20 rebate, however, this also applies to the 1% foreign transaction fee charged by Visa (only with ATM withdrawals unfortunately, debit card purchases in foreign currency are not refunded the 1% fee) Update: seems they do refund any purchase - the rep said it was ATM only but after around a month the foreign transaction fee for a purchase I made was refunded. Wire fees, and other bank fees. Alliant's $20 rebate does not include the 1% Visa foreign transaction fee or other fees, it just includes ATMs operator fees.
A con is definitely that the savings rate is only 0.5%. The checking offers 0.5% too; it also offers a rate of 1%, but this requires 10 debit card purchases each month.
Depending on where you are in the world, they ship debit/credit cards from different offices around the world so they get to you faster. They let you lock/freeze your debit card. They also have live chat on their website, email, 24/7 phone support and toll-free numbers for many countries around the world so you are not charged a fee to phone the US, however email is the same as Alliant's online message center, it always takes at least a day longer than they say it will.
An interesting feature is when paying with the debit card, if you live outside the US, you use the address of UNFCU's HQ as the billing address, so even if you don't have a US address you can still access things that require a US billing ZIP, however this can be a nuisance as you literally can't use your own foreign address with the card, you have to use the HQ address. They do have maintenance warning messages, however not as much as Alliant, and I personally have still been able to log in during those times.
A small thing I appreciate is that they seem to promote the 'member' aspect of a credit union more than Alliant; Penfed I haven't used enough to comment on in regard to this. UNFCU sends reminders about the Annual General Meeting and even offers cash prizes for voting for candidates for the board of directors. On their debit card, it also mentions 'member' while Alliant's mentions 'customer', which to me says quite a bit. Alliant in my experience sees itself more as a fintech than as a member-focused credit union, reinforced by the fact that on the membership application there was a really small box you had to check if you didn't want to have members of the board use your vote during membership meetings via proxy. UNFCU seems eager to give members a say, while Alliant appears to be hoping they won't notice the small proxy opt-out box and they can use their votes how they see fit. Again, I know that is small, but I like the member-focused aspect of credit unions and that difference stood out to me.
Hope my experience from a non-resident perspective is helpful!