A good percentage of owners here have multiples. Lots have singles. Is either better? Nope.
I have two dogs because my husband needs a buddy. He was really lonely when we had 1 dog who was ridiculously bonded to me. I added the sheltie more for myself than for Shay. Melli became my little trooper and my husband got "our" boy to be "his" boy. Both dogs adore both of us, but there is a clear favorite happening. We had this happen with the original 2 Aussies -- he was jealous that #1 was so tight with me and wanted his own #2. Then again when we had Aussies #1 & #3. #3 became my minion and #1 gravitated to my husband.
As for dog - dog interaction. Honestly, I have never had dogs super tightly bonded, but I always adopted adults except for the one pup. They dwelled together and kept company by presence, but it was not best buddies, romping partners, pals. Just roommates. When Aussie #3 passed, Shay who was raised by him said, "Mayson who? It's all about mmeeeeee!". He was quite happy that way. Clearly perfectly happy that way.
I do know that when I was at the vet's this last week handling the two together was really a challenge for me, but one is a larger dog. The OP of this thread really had a hard adjustment with these two siblings. She adores them but they brought a level of chaos she wasn't ready for in the way of barking, romping, change in the way she trains, etc.
Multiples are great, but the dynamic is different. It's something to really think about. Do you have a lap for both or will they both vie for attention and be jealous? Do you intend to train or otherwise work with them? It's actually really hard to go off with one and the other is left at home ticked off (unless you have one that sort of belongs to a spouse or other human resident). Can you handle the extra barking, rough play, and chaos? Financially can you double everything? Gender choice also plays a role -- you have a girl, a boy might be a better 2nd choice. Girls get along but it is a totally different relationship and sometimes can be a bit ugly. How bonded is your pup to you? Lots of dogs who have the "it's all about meeeee" attitude would be happiest that way. There are less dominant dogs who seem almost lost and leaderless without someone to sort of guide and cue them though. Will this change how much the dog/dogs are left home? For instance I took my boy everyplace -- meaning I took him where I could and then let him visit my mom during errands when I couldn't. Now with two, they both stay home or one stays home with the husband and one goes with me. Does this change anything like travel to hotels or camping? Two sometimes aren't welcome places.
There is much decision into adding a 2nd dog. It really is a preference and sort of a checklist of yes and no for each person and family. Sometimes it might just be better to find good training groups (after shots are complete) and go through puppy class and obedience and agility and ... together as team and get the socialization and exercise and stimulation that way. Other times, having a pair is a brilliant thing.
I know for my house we have to have his and hers dogs. We are very unbalanced any other way. If I were alone, there would be one only, but I work from home so the dog is with me 24/7. My first Aussie clearly preferred a companion as we both worked outside the home and went to music gigs on weekends too. They weren't really that interactive and tight with each other, but they were present as companions and sort of roommates.
Best wishes on your decision. Either way is right, just very different.