Lynn

I am assuming that since you are replacing lilac bushes you want a flowering perennial plant that is hardy and not terribly susceptible to insects and other pests.  Also to be avoided are popular but invasive plants like the butterfly bush.

There are a number of choices.

The shrub that is probably the most hardy and resistant is viburnum. It is a fast-growing bush that is covered with blooms in spring and early summer and is resistant to pests and mildew.

Azaleas come in a variety of colors and are very popular and hardy in Delaware. They are susceptible to lace bugs and other insects and do need some care to prevent insect problems.

Rhododendrons are similar to azaleas but tend to be larger bushes.

Mock orange plants are hardy, fast growing pest resistant plants with very fragrant white flowers.

Hydrangeas are attractive fast growing flowering plants and come in many interesting verities. It is important to know their blooming characteristics so that they can be pruned at the right time.  They prefer partial shade (half day of sun) and need to be kept moist.

Crepe myrtle is a very popular, hardy plant in Delaware that comes in a variety of colors and blooms late in the summer. It tends to become treelike unless pruned annually. It has been a pest free plant until the last few years when crepe myrtle scale arrived in Sussex County.  If left untreated it can kill the plant. It can be treated with horticulture oil and/or systemically through the roots.

Most of these plants are not bothered by deer but there are no guarantees. Deer are known to change their taste during cold snowy winters or when their environment changes, such as when it is disturbed by new development. They have been known then to munch on plants that they ignored for years.

These are perennial plants that I have had experience with. There are other flowering plants that are available from green houses and other locations. Beware as there are invasive plants that are not allowed in Delaware that are sometimes still sold at these places.

I hope this helps

Tony