While it is politically correct to use manual shears for trimming around the house and flowers, your back and knees will do you in.

For your size of lot I would recommend getting a good electric string trimmer. I say electric because I doubt there is anything that requires trimming on your lot that is more than 100 feet from an outlet. With electric there is no gas tank, mixing gas, or starting problems, just plug the drop cord into the house pull it to where you are trimming and pull the trigger. PS My old Craftsman electric finally died after about 15 years.

If you are bound to use the manual I would recommend getting one that has a long handle so you can stand up and do the cutting. Remember the back and knees.

Just to piggyback on this question...how can one sharpen manual shears? I've been trying to figure it out, but am not sure...?

In the spirit of the manual reel mower, what you are looking for is a flat spade, and is sometimes called a manual turf edger. You can find it where gardening hand tools are sold. It has a 3-4 foot handle and a flat square blade about 5" wide at the bottom of the handle. I have used one for years for just that same purpose (although now I use a reciprocating edger), and I still have the original flat spade I purchased nearly 20 years ago.

Search Amazon.com or other source for "edging shears". These are long-handled tools that have shearing blades set vertically or horizontally. They are great for small areas, and less trauma than a string trimmer. These tools seem to be imported from England or Australia, and you are not likely to find them at your local store.

We had a pair of the right angle shears in my childhood home for as long as I can remember. Most likely just bought at a local hardware store in the 50's or maybe even before. Used for at least 40 years, probably still going strong somewhere.

I bought a pair for my own home recently. Two months and the handle broke. Just venting, but this seemed like a good place to do it.

Quercus, you're reminding me of an old tool I used to use--the long-handled shears that saved you getting down on all fours....I imagine you can still find them in the garden tool section of a hardware or nursery.

I'm always trying to visualize what size of lawn people quote by giving square footage and I do that by square rooting.
And 3000 square feet can be looked at as 55 by 55...and by any standards that aint so small.
I think you should re-evaluate what a string edger can do - they can be used in many ways. Turn them on their side--and make a nice clean edge to a garden at the lawn; they can, tear out weeds that dare to invade your garden; they are easy to navigate around posts and flowers--with care--and can be very satisfying once you look back on your use of it.