Hey Mike,
In my past roles I've used a bunch of different options - 1SC, Infusionsoft, our own in-house solution included. I also spent several months researching different platforms as part of my day job.
Short answer? It really depends on your needs (sorry if that's a cop-out.... I'll expand a little...).
Before I get onto some specifics, I feel compelled to share a particularly bad experience we had with one platform - Infusionsoft. This was a few years ago now, so perhaps they have radically changed their model (and software) but at the time we had no end of problems. And by 'problems' I mean business-threatening problems... for example, on one occasion (following an update to their platform) they automatically re-billed tens of thousands of dollars to our customers' cards without anyone's consent.
The platform was flakey, the reporting was dire, the support was lacking. I remember a well-know Australian marketer (who I'd warned about our own experiences) telling me "I know... you told me so..." on having had a similarly bad experience.
As I say, I appreciate things may have changed since then but I would strongly advise that anyone considering Infusionsoft look past the slick marketing and do plenty of search/research to find out what other marketers are saying right now.
Following our bad experience we developed our own platform, in-house. Great for flexibility, but expensive - and there was some lost sleep on occasion when the platform went down (our responsibility... a negative for any smaller operation).
Since striking out on my own last year, and as a smaller operation myself, I looked again at a bunch of platforms - 1SC, Nanacast and PWC included - I ended up choosing Ultracart, and I have to say I 100% recommend them.
The reason I went with them was a combination of things, including:
1. Feature-set - pretty much everything you want (or will want) to do is possible.
2. Digital-product friendly. 1SC makes it hard to sell software products, since you have to deliver the file via their platform, and there's a puny file-size limit. They ruled themselves out for me right then and there, and their pre-sales team were unable to figure out a solution - something I found disconcerting, as I know I'm not the first to query them about it.
3. Quality - on the surface, Nanacast sounds like it has a very comparable feature-set, but I found the interface clunky and uninspiring. In fact I found it so basic that I found myself questioning the platform, period. Note: I do know some marketers who rave about Nanacast, but my guess is that it's best suited to operations with a resident 'tech' rather than those of you who will be using it yourself.
4. Integration - not just payment platforms (I use a credit card merchant account and also Paypal) but also other extensions (I use AWeber and AMember for mailings/memberships with no problems at all... and there are plenty more options besides).
5. Customization - cart skins, urls, affiliate resources, secure URLs... everthing's easy to make your own.
6. Price - obvious, but UC is very affordable, and scalable.
What's more, despite being based in the UK, I have found the support to be knowledgable, prompt and efficient.
Sorry if these thoughts come across as some kind of promotion - I should note that I am in no way affiliated with UC at all - I guess I am just trying to share my experience in the hope that it might help fellow JVNP2 members avoid costly mistakes.
Happy to answer specific questions about the platforms mentioned if you message me.
Rich