I just started about 3 months ago, and got my sis hooked about 1 month ago.
For your typical smoker, the little slim is close in appearance. I started with 1 65 and 1 78, both auto. If I had to start with x2 batteries, it would have been awkward. I added a 78 manual pretty quickly. Even with 3 batteries, the constant swapping, and fear of running out when I am away from a plug made me move to an x2.
My sis was adamant on the shape. So I gave her my little batteries. Even though I told her the 78 would last longer, she insisted on 65's, so I ordered her one. Now she complains about the charge only lasting 1 hr, and taking 2 to charge up. So I got her a second charger, so she can be charging 2, vaping 1, and 1 on stand by.
Finally, I got fed up with it and bought her a pink x2 650 for xmas... She went from hating big batteries to loving it.
The moral to the story is once we start vaping, it is easy to recommend the best options. However, getting over preconceptions, and getting friends to start vaping is the key. If it is easier for them to take the leap with little white 65 auto's, then do it.... Once they start complaining about charging and rotating batteries, point them to the x2's. It is a good step up, and you retain compatibility.
If you have the funds to do it, "buy back" the little 65's, and sell them to other friends to help them quit... you can do this multiple times.
In terms of length, the 65 + standard carto is already the length of 100's cigarettes. The capacity of a regular carto will exceed any small battery.. Going to a long carto doesn't add much value to a person just starting out. OTOH, the 78 battery might be worth it.
The most important thing is to get them to give it a try. While a white auto 65 + regular carto is not good for regular vapers, for a beginner, it could be the easiest transition. If you have more advanced hardware, once they are vaping, you can explain pluses and minuses, and help them move up. It worked for me, and my sister....
Sorry for the long post, but I think the hardest part is getting smokers started, after that... that's when the fun begins.