The work would be almost exactly the same, as both companies are third-party vendors for the same company. I have only worked at Air America but I know that one major difference is at SkyLens you would be a W-2 employee, while at AA you would be an independent contractor (which of course has its disadvantages). Another difference is Air America pilots get scheduled time off during the season (2 one-week relief periods), while as far as I know SkyLens pilots do not. Besides that there are likely some differences in pay and company structure. For instance, SkyLens appears to pay a daily salary (
http://forums.jetcareers.com/threads/skylens-hiring-for-2015-16-season-new-low-mins.223120/ ), while Air America pays by the Hobbs hour but with a daily minimum guarantee for if you don't fly because of weather, maintenance, ATC denial, etc. Also, SkyLens provides a single-occupancy hotel room and rental car directly, while at Air America you would receive a daily per diem to cover these expenses. This can be nice since any per diem you don't spend is yours to keep, but it can also be a disadvantage if you end up somewhere expensive by yourself (since we would often share expenses)- like happened to me when I was by myself in the Bay Area and then Seattle for about a month my first season. Since both companies do the same kind of work, both have a season starting around October and ending in May or June, with some work during the summer (but not as much and it can be hit or miss).
I enjoyed my time at Air America, made more than I could have at just about any other job I could have gotten with the experience I had when I started there, and got some good flying experience out of it as well. I have not met any SkyLens pilots in person, but some other Air America pilots have run into them on the road and from what I hear it sounds like a good company to work for as well. Also, the SkyLens pilots who post on this board usually have good things to say about the company. Either company would probably be just fine to work for, and I would probably apply for both if I were in your position. However, chances are neither AA nor SkyLens will be hiring until around September, when it is almost time for the 2016-17 season to start.