We are 4 friends who are planning to stay in New York next April or May for 4 or 5 days.
We would then like to rent a car and travel to the Cape Cod area ( or any other suggestions) for about 7 days.We would like a nice route to get there and touring suggestions. We will drive back to New York for our flights back to the UK., so perhaps a circular tour ?

well Cape Cod is wonderful in the summer but at that time of year will be chilly - and the water icy. I would do Boston instead - and perhaps see some other sights in Mass. If you want to beach you need to head far south for that in Apr/May. (In NY out beach season officially begins the Memorial day (last weekend in May) but the water is still cold - North Atlantic - not warned by the gulf stream as in europe.

May will be better weather in New England than April. It can still snow in April, especially in northern New England. April is also mud season in more rural areas. Rain is likely in early to mid-May as well.

Flowers will be blooming in the latter half of May. In the Boston area some of the more popular tourist sights might be overrun by school groups on field trips, though. Still, I would plan your visit as late as possible if you want to see New England.

Well, as a lifelong New Englander, I think there is something to be said for walking deserted beaches off season, as long as you bundle up and know what you're in for. Apr/May can be really cold or just chilly or even moderate, wet, dry, snow in the mts. Same for NYC.

Would be helpful for us to make recommendations if we know what you're looking for - scenery, does weather make a diff, what are your expectations, mts or coast, etc.

May is definitely preferable to April when it comes to New England. It's actually one of my favorite times of year because most of the vacation areas are pretty quiet, until Memorial Day weekend at least.

If you do go to the Cape, stick to the "Outer" Cape, especially Truro/Provincetown. This is where the real majesty of the Cape lies, with the quaint towns and the National Seashore. I'm also partial to the towns along Route 6A, which are generally more charming than the busier resort towns on Nantucket Sound. 6A would be the most attractive / interesting route to get to the Outer Cape, rather than the highway-style Route 6.

Still, as others have mentioned, May isn't exactly the most popular time to visit the Cape, in part due to the unpredictable weather and because you can't really swim in the water (unless you're very, very brave). Boston is a fantastic city and would be a great alternative unless you're looking for a more relaxing destination, which I completely understand (especially after the chaos of NYC).

Whatever your final destination, I would recommend stopping at two places along your route from NYC: a short stop in Mystic, Connecticut, to see the Seaport; and Newport, Rhode Island.

Newport definitely warrants an overnight stay and could easily take up a multi-day chunk of your vacation if you wanted. The old town is gorgeous and there's plenty to do, and you're a short distance from all the beautiful enormous mansions and the scenic Cliff Walk. Easy side trips to beautiful Jamestown and Beavertail State Park, charming villages like Wickford, and the capital city of Providence with its enchanting College Hill neighborhood and lively downtown core only sweeten the deal.

If you're looking for something a little more off the beaten path, then Vermont and New Hampshire offer some beautiful mountain scenery, but I would only recommend going in the second week of May or later (before that it's still mostly brownish or even snowy). Vermont is more bucolic and pastoral with rolling green hills and dairy farms, while New Hampshire is a little more rugged in its mountain scenery (think Scotland) with some beautiful, large lakes.

If you're interested, look into Stowe or Woodstock in Vermont, or Meredith / Lake Winnipesaukee in New Hampshire.

In the Concord NH area, apple trees bloom around May 15. We've visited the Cape in April when thousands of daffodils were blooming along the roads. May can be a beautiful month unless you want to go hiking in northern areas since it's also black fly season. Yes, it can snow in April but March is mud season. That's when the ground is finally thawing and dirt roads can get muddy. If you aren't driving on a dirt road, it doesn't matter, but some consider it a dismal month.

Perhaps you would like a cities tour, then Boston and Newport are great choices. But, I agree with Irishswampyankee that spring can be a great time to be outdoors before the tourist season starts. I'd choose May because it's a prettier month but it can be cool and drizzly or have some early hot weather. I suggest also including Portsmouth NH, only an hour north of Boston. Check to see if harbor cruises are operating that early. Take a culinary tour of Boston's Chinatown or North End Italian neighborhood.
It would really help to know your interests.