Two weeks or longer? That's when a flat pulls ahead

For a long weekend, there's not much in it between a hotel and a serviced apartment. Stretch the stay past a fortnight and the flat starts winning, first on the nightly rate, then on what you spend eating, and eventually on something harder to price, which is having a normal week.

The rate, and the tax after four weeks

Most residences price by length of stay. A week usually gets a lower nightly rate than three nights and a month lower again, and a few of the residences we list only take bookings of four weeks or more. When you ask for a quote, ask for the rate at one, two and four weeks, because the steps are where the saving is, and adding a couple of nights to cross a threshold sometimes costs next to nothing.

Past four weeks, tax can shift too. In places HMRC treats as similar to hotels, VAT from the 29th night of a continuous stay applies only to the part of the bill that isn't accommodation, with at least a fifth counted as facilities. Not every serviced apartment building qualifies, so ask the residence.

Starting rates typically sit around £270 a night, so on a three-week stay even a modest weekly discount adds up to real money. Ask about the cleaning frequency and the terms for extending while you're at it, and if the stay touches July, August or December, book early, because the bigger flats go first.

Eating, working and washing at home

In a hotel, you buy every meal. Three weeks of hotel breakfasts for two, plus room-service suppers on the nights you're too tired to go out, can easily cost more than any difference in the room rate. A kitchen doesn't mean cooking every night; it means porridge at seven, a sandwich at your desk, a bottle of wine in the fridge, and eating out because you want to rather than because there's no choice. Book a supermarket delivery for the evening you arrive and breakfast is sorted.

Working from a hotel bed is bearable for a couple of nights and wearing over two weeks. A one-bedroom flat, which most residences offer, gives you a living room with a table, so the laptop lives in one room and you sleep in the other. Check what the work surface actually is, since a dining table for four with a proper chair beats a narrow desk wedged beside the bed, and a two-bedroom flat gives you a door to shut for calls. People mention that separation after a long stay more often than they mention floor area.

Hotel laundry is priced per shirt and comes back tomorrow. Most serviced apartments have a washing machine or washer-dryer in the flat, and some buildings add laundry facilities or a service on top, so you can pack for one week rather than three. Bring a travel-sized detergent for the first load.

The routine becomes yours, too. There's no breakfast cut-off at 10.30 and no knock at nine, and cleaning happens on set days, usually weekly or twice a week, so you know when to be out. The neighbourhood slots in around it: a coffee place, a gym, a dry cleaner, a Tube line to the office. Nearly all the residences are within about ten minutes' walk of a station, so choose by the journey you'll make every morning.

Where a hotel still wins

Most serviced apartments have no room service and fewer staff. Only about half have a reception desk, and daily cleaning is rare. If you want someone to carry your bags, press a suit by 8am and book dinner every night, a hotel with a good concierge does it better, and for four nights with every meal out the flat's advantages mostly vanish.

Travelling as a family or a group? Why a flat works better

Put a family of five in a hotel and you get several rooms down a corridor, with nowhere to sit together once the children are asleep. Three couples on the same trip have the same problem. A serviced apartment puts everyone behind one front door, and by the second morning you'll have noticed the eight differences below.

The first is separate bedrooms behind one front door. Parents get a door to close, and teenagers get a room that isn't also where everyone else sleeps. Most of the residences we list offer two-bedroom flats, and a good many do three. Count the bathrooms as well as the bedrooms, though, because two bathrooms between five people is the difference between a calm 8am and a queue on the landing.

The second is somewhere to sit after bedtime. In a hotel, once the children are asleep the adults are left sitting in the dark, or in the bathroom. A flat has a sofa, a television at a sensible volume and a door between you and the sleepers. Sofa beds there are handy for a fifth guest, but the room closes when that person goes to bed, so for more than a night or two an extra bedroom is worth paying for.

Multi-generation trips are where apartments win outright. Grandparents want their own bathroom, a lift or a ground-floor flat, and somewhere calm to retreat to in the afternoon. For a wedding or a big birthday, plenty of residences have several flats in one building, so a family can book two or three on a single enquiry and still keep separate front doors. If the building allows it, ask for them on the same floor.

Big flats are the scarce ones. Only a couple of dozen residences go to four bedrooms or more, and they're booked first for the summer holidays, half-terms and Christmas. Bringing the dog shortens the list again, since most places don't take pets, and outside space is rarer still, so a terrace for the children to charge about on is a find rather than an expectation. On a group trip, book the big flat first and plan everything else round it.

A kitchen means fish fingers at half five, a bottle warmed at 3am and a cupboard stocked with the one cereal they'll actually eat. Central London restaurants are generally good with children at lunch and rather less so at 8pm on a Saturday, so being able to feed the small ones at home and eat out as adults once they're down is probably the most useful thing on this list. Book a grocery delivery for an hour after check-in and the first evening takes care of itself.

Children also go through clothes at a rate no suitcase allows for, and with a machine in the flat you can pack half as much. Washer-dryers are slow to dry, mind, so ask for a clothes airer too. It changes group trips as well, since friends sharing a flat can run one wash for everyone after a wet day's walking instead of each paying hotel laundry prices for a pair of jeans.

You pay for the apartment, not per head. The residence sets how many it sleeps, and within that limit the price doesn't change. Starting rates typically land somewhere around £270 a night, so split a two-bedroom between two couples and put it next to two hotel rooms before deciding which is dearer. Do check the maximum occupancy, because some places charge for an extra guest on the sofa bed.

Most residences can supply a travel cot and a high chair, but they don't keep many, so ask when you book. With a baby, the bigger question is the building. Only about half the residences have a lift, and carrying a pushchair up four flights of a converted townhouse gets old on day one, so ask which floor the flat's on before you pay.