30 days stay - vacation/work in Europe

@Kaeleku
Thanks for the reply. We do a lot of traveling but never had to work while traveling. We both work in IT so fast reliable WIFI is def #1 requirement. Good to know booking.com has ranking.

We thought about SE Asia and eastern Europe as well but we'll be working on pst time so the time difference would be too much. We may need to rethink #4. #5 is negotiable if we find a place that has #1-3.

-Vann

Portugal remains a little cheaper than other parts of Western Europe. So look at Lisbon or Porto.

Check the time zone. A lot of "eastern" Europe is on Central European time. Portugal's on "Greenwich" time adjusted for DST

One of the main issues you are going to find in most places in Europe is that September is still a busy season and accommodation prices and availability will reflect that. Eg Portuguese schools don't return until the second week of September.

Many places in summer holiday destinations offer great value monthly winter lets, but these run from November through to March. I am paying £600 total for a 29 night March letting in the Algarve of Portugal, but the same 1 bed apartment lets for £475 per week in September.

By now, many places will have taken some lettings for September, so your choice maybe more limited.

You should just about be able to find accommodation in the Algarve for your budget. The weather will still be decent, but it is short on your point 3. Hiring a car is very cheap too.

Budapest would fit all your criteria as would Prague and most of Central Europe, but there would be more of a time difference. I have found some European apartments have a strong wifi signal, but they have a limit on the data download per month, which has run out whilst I was there!

The only country on GMT in continental Europe is Portugal, besides the British Isles, of course. All the rest, from Spain to Poland, are on Central European Time. Greece, Romania, the Baltics are on Eastern European Time. Most of "Eastern Europe" is in the same time zone as the major Western European countries. It is still a 9-hour difference to PST, though. A 9-to-5 workday will be a 6PM to 2AM workday, 5PM to 1AM in Portugal and the UK. Luckily, Portugal is one of the cheapest Western European countries and fits the other criteria, too - look at Lisbon but Porto is better value for money IMO.

I've spent 7-1/2 months in Europe over the last two summers, staying primarily in hotels. In my experience Wi-Fi signal strength definitely varies considerably, so that's something you'll have to really focus on when you read reviews. No city is safe in that regard. I had one quirky experience in an apartment in Bulgaria: My Samsung smartphone connected readily; my Samsung tablet would not connect at all.

I haven't been to Budapest recently but suspect that it might match your criteria. Otherwise, I keep thinking of Barcelona if you're flexible on the cost. There's everything from medieval to modernista (art nouveau) architecture, lots of museums, active nightlife, plus many good day trips when you have spare time. But the city is trying to crack down on illegal apartment rentals, which could complicate matters for you. If Barcelona makes your short list, you might post a separate inquiry in the Spain forum with something like "Apartment for One-Month Teleworking Stint in Barcelona?" as the title. Enric will probably see it and comment.

Have you considered staying in different countries? You could fly into Lisbon and out of Rome and travel through Spain and France in the process. Spend 9-10 days in each country. Move around and get a real feel for each place.

Romania is said to have excellent internet and it's very affordable.

Internet service varies greatly in apartments. I would not recommend sitting in cafés, since these connections are public and very often hacked. This goes for any other WiFi hotspot, too.
It's just something that we have all learned to tolerate.

I'm thinking Berlin might be too expensive. Maybe not? September isn't a bad month almost anywhere. Krakow, Poland comes to mind as a place that's lively and affordable. I'm thinking you can probably pick any college town in a more affordable country. Spain and Poland are the cheapest I've been to but I haven't been to Hungary or Balkans yet. Poland has cheap trains to get around, Spain has cheap buses that will get you anywhere.

You specifically mention Spain, France, Portugal and Italy, so I will respond with those countries in mind.

All these countries have wonderful opportunities for great travel. Portugal is a small country but filled with great places to see. Lisbon and the surrounding area are with 6 days when you take a day trip to Evora, then Sintra, Cascas, Obidos and Batlia Cathedral.

Porto is great, plan on two or three days there and consider a cruise on the Douro River. Wonderful and scenic.

Also, Portugal is cheaper than the other countries you mentioned.

Spain, I would start with the Madrid area and make sure you take day trips to Toledo and Segovia. Then take the train to Seville and spend some time there, perhaps visit Cordoba and Granada (although Granada is some distance from Seville. Barcelona is another place to see in Spain, and you could fly there from Seville.
You could easily do Spain and Portugal in one trip.

France has so much to offer, even if you don't go to Paris. Spend a few days in Paris and consider the following areas:
Normandy
Loire Valley
Alsance (Strassbourg next to Germany)
The Rhone River, Burgundy and South of France.

France is a bit more expensive than the Iberian countries.

Italy has the big three, Rome, Florence and Venice, but consider Siena, Pisa, Lucca, Ravenna, the Naples area with Capri, Sorrento and the Amalfi Coast. Also, in the north there is great scenery in the lake region on the Swiss border.

The smaller cites you would need to take a day tour from Rome, Florence, Venice or Naples.

If you love ancient history, then Italy is the place, a week in Rome is needed and the Sistine Chapel and St. Peter's is awesome, aside from all the ancient ruins.