As a small outfit, I find that mowing is always more profitable in the long run. I usually only provide this kind of work for existing customers or commercial accounts or where lawn work will follow.
For instance I manage the lawns for one of the McDonalds franchises. One store was in terrible shape bed wise as the landscape contractor let the property go. I parlayed that into a nice bedding reinstall and maintenance contract with my customer for ALL the properties. It worked out like this: he paid separate rates to get the beds back into maintainable shape and now pays a monthly maintenance fee to keep them that way.
The formula that works best for me is to hire (experienced) help for larger bedding jobs so that I can finish quickly and still make a decent profit without breaking my back. I bid probably more than than average outfit because I don't typically want these types of jobs. So when it works out, I am not left wishing I had not taken the job or underbidding myself which is easy to do as we all know. The trick is not spending too much time on the estimates so that my time is wasted. Thankfully, this does not happen very often.