It really depends on how actively you want to participate in managing your account.
I'm not too familiar with Janus but I imagine either they (a) have pre-made portfolios categorized by levels of potential return and/or risk or (b) create custom-built portfolios designed to match your specific needs (i.e. how much risk you're willing to accept). In either case, you're going to pay a premium for that service. The benefit is that if you don't follow the market that closely or if you're not very knowledgeable about how to invest they will (most likely) get you a better return than you could get on your own. Another benefit (especially if you're just starting out) is that they can get you a wide selection of stocks/bonds with minimal trading costs. I'll skip the lesson regarding diversifying individual stock risk (leaving you with just market risk) by investing in a large number of stocks (~20). If you manage your account by yourself, chances are you'll spend at least $200 in trading fees just to get to that level. A company like Janus can probably get you a good selection for less. (That said, many sites like
TD Ameritrade and
E-Trade will give you credits for free trades to be used in the first 30 days after you open your account; this can significantly reduce the costs required to get started.)
I've managed my Roth IRA through
TD Ameritrade for around 4 years and thus far it's suited me pretty well. I have a pretty big aversion to paying someone to do something that I can do myself. However, I have little way of knowing whether I have done as good (or better) of a job as a professional.
Buy low, sell high