Hi all - I've done searches here, TPG, Reddit etc...but I'm still confused, between Boundless and Brilliant (nothing that AF is almost the same after the credit), can anyone confirm that you can't get both sign up bonuses...24 months out or ever? I read maybe you could get the business card bonus but I'm so incredibly confused.
My situation: I currently plan on using one of these Bonvoy cards to book my hotels and also plan on using the Delta Reserve for flights and other everyday purchases (personal and for work). I spend a lot for work monthly (all can be done on personal cards and reimbursed) and between events, office supplies, flights, and hotels (I travel 1-2x a month exclusively with Delta/Marriott and already have Global Entry, TSA Pre Check, and Clear), I'm still not sure which Bonvoy card to get in order to maximize. We don't really travel for personal reasons since I'm already gone so much, but would like to change that in the future 
The one reason I'm leaning towards the Boundless is because the Reserve is Amex and we travel internationally 3-4x a year to Asia and Europe (ok we used to, I know with the state of the world that's tbd but say hypothetically) so I figure for those trips I'd need to stick with Chase to pay for things and get points since most places don't take Amex and why use cash/debit cards (large amounts of $ for big groups of people). Is that accurate in your opinions?
Any input on trying to maximize the welcome bonus between these two cards? I don't plan on churning, I truly think I'd use these 2 cards to use in a straightforward way to get some rewards on high monthly spending but want to ensure my bases are covered domestically and internationally.
You can get SUBs for both cards if you have not received a SUB or upgrade offer on the other within the past 24 months. You will not be approved for either one if you have been approved for the other within the past 90 days, even without a SUB. Both the Amex Brilliant and the business card have the same limitation there.
If you will use the free night certificate up to 50k points, the Brilliant is absolutely the way to go as it is far more valuable. I used mine for Ritz-Carlton in 2019; the cash price would have been over $700/night. Combine that with the $300 statement credit and I got over twice the value of the AF. Unless you are only staying in lower category hotels, there's a clear winner as long as you are staying in Marriott properties at least a few times a year anyway. Any and all Marriott cards give you 15 nights (total, whether you have 1 or 20 Marriott cards) toward elite status, and getting those extra 15 is certainly helpful if it means the difference between Titanium and Platinum or Platinum and Gold. If you have to choose 1, I'd go with the Amex. If you can justify two and aren't worried about not receiving the SUB on one, go for both with at least 90 days between them.
As for the Visa/Amex debate, unless you are getting outsized value (like in the pre-SPG merger days from earning SPG and spending Marriott) from Marriott Rewards (or if you're getting Platinum status through spending $75k on the Amex) it may not make sense to throw everything on these cards and you might be better served with a Chase Sapphire Reserve (or Preferred) or similar card for the times when Amex is not an option. I personally only use my Marriott card for Marriott stays - with status, that's 23.5x points per $ and it adds up fast. (Edit: You mentioned having Delta Reserve. With the value of SkyMiles and depending on how much those MQM bonuses are worth it to you, you'd be far better served spending on that than the Marriott cards. My current strategy for 2019 and 2020 is that all non-category spend goes on Delta Reserve to get additional MQMs.)
60k is elevated (usually 50k) for CSP. As long as you have no doubts about receiving at least a $10k starting line, I would strongly consider CSR instead even though the SUB is only 50k. Look at the benefits and earnings for both and do the math. In most cases, CSR will make more sense even with the higher AF. Do note that you'll need to be under 5/24 (or have something that overrides it like a green checkmark offer in your Chase account or an in-branch preapproval) in order to open either card.
You're in luck that this forum is pretty Marriott and Delta heavy. 
As a Delta flyer, you have a few options with Chase Ultimate Rewards. You can use them in the travel portal to redeem for airfare and both cards have a bonus multiplier. You get a 25% bonus with CSP and 50% bonus with CSR. So effectively, a CSR earns 4.5% back toward airfare for travel and restaurant charges and 1.5% for everything else. (CSP would be 2.5% and 1.25%.) Alternately, you can move your points to either Air France/KLM or Virgin Atlantic and redeem for award flights on those airlines, Delta, or any SkyTeam partner with AF/KLM. If you can get direct flights from your airport, booking Delta One flights through Virgin is an absolute steal (and Virgin Upper Class isn't bad at all). Alternately, URs transfer 1:1 to Marriott. If you wanted to invest more in Chase, the Freedom and Freedom Unlimited cards can be great siblings to CSP/CSR for racking up URs with Freedom's 5x categories and Freedom Unlimited's 1.5x across the board.
Lucky me Because I'm super new to this all and thus, super confused.
Interesting about the Virgin booking - I'm near a major hub and do have lots of flight options. I just wrote it off because it was so confusing to me with partners and since most of my trips the past 2 years were work related, I booked through Concur on a corporate card until someone asked what the heck I was doing when I could expense and get points.
I probably wouldn't get a lot of points on the Chase Preferred/Reserve - I'd probably just use it as my international card when the Delta Reserve/Marriott cards didn't work. Do you think the CSR is worth it as a backup - some of the perks seem to overlap with the Delta Reserve. Or would you recommend it not be the backup and instead primary? Now my head is spinning