Having a modular framework like OSGi at the client side is a huge advantage when doing remote management, because it gives you much insight into what's happening inside - installed bundles, dependencies, states of the bundles, available services etc. This helps a lot when you have to solve a problem remotely. Another advantage is that OSGi basically forces programmers to develop proper modular and dynamic systems, which makes (remote) updating much easier.
So, if you have to decide now what language and framework to use for the client side, I strongly recommend OSGi for the embedded and mobile clients. For the PCs (I guess you mean desktop PCs?) this is probably not the best choice - it depends a lot what you want to achieve there. If you want to install MS Office remotely OSGi won't bring you forward ;)
However, if you already have existing programs at the client side and are discussing whether to convert them to OSGi, I would recommend to investigate some time first to see whether they can be converted easily. Some software packages could give you a lot of trouble converting to OSGi, not because OSGi is complex, but because the program itself is not modular and has a lot of assumptions about the static nature of the environment (e.g. nothing ever disappears, parts of the system never get updated etc.). The irony in the matter is that these are exactly the programs which will give you most trouble later anyway no matter which remote provisioning system you chose.
If you have OSGi at some of the targets be sure to use a remote provisioning system which gives you access to the full OSGi functionality and not only the most basic and simple install and update functions. I haven't yet used Apache ACE, but I have experience with another provisioning system - mPower Remote Manager. Here are some snapshots from the documentation which can give you a feeling what is possible with OSGi as a base - you can draw your own conclusions whether it will be useful for your case or not.
