For me it goes:
1) Ash, Serena, Clemont and Bonnie: Surely a very unpopular opinion, but I loved this group. Yeah sure, they might have been a bit light on the banter side, but they made up for it in how close the overall group felt. Ash finally acting as the leader of the group (and still keeping his airheaded tendencies, such as being gullible to science), Bonnie being a surprisingly endearing kid character (coming off Max), Clemont providing the comedy and with his own decent development till his gym (slowed down after that, but got good development again in the Flare arc), and of course my favorite Serena, who started off really shy and unsure, but visibly showed her getting more confident in the group. The scene in XY067 where everyone places their hands on each other was a really great moment for me, and highlighted the family like bond they had.
2) Ash, Misty and Brock: The OG classic, and can't go wrong. The humour and teasing was hilarious, and when needed, there were so many moments between them that highlighted how tight knit they were.
3) Ash, Brock, May and Max: I hate Max, but as a group this was also very good. Ash and May had that student - mentor vibe, and Brock was still great, with Max providing the occasional funny sarcastic remark.
4) Ash, Cilan and Iris: Surprise! Now the less said about this series the better, but as a group, I thought these three were pretty good. Cilan and Iris definitely bounced off each other well, and after Brock really got boring in DP, I especially liked Cilan who felt like a breath of fresh air.
5) Ash, Dawn and Brock: Ash and Dawn probably had some of the best chemistry, but that was it, as Brock unfortunately became so boring and unneeded. Barring preparing food, you'd probably forget he was an active part of the group (other than Croagunk occasionally reminding us), as DP was all about Ash and Dawn.
6) Ash, Misty and Tracey: Luckily Tracey only existed for one season, as he was just bland and unnecessary. Ash and Misty interactions felt lacking too, compared to OS, as the absence of Brock was really felt.
7) Ash and a bunch of school kids: Sorry to say, but I really dislike this group. In all the previous series, no matter how good or bad, the groups felt like they were important for each other and had an impact on them. But in SM, it just feels like a bunch of school kids you meet for a while, and easily forget about once you leave. Everyone's always so happy, other than during the AF arc, where they appeared for the last two episodes without doing anything previously, and Sophocles has the nerve to say that they were the best team.