I think the best advice is to grow what you prefer to eat. And if it's practical to save your own seeds, all the better, because they're getting more and more expensive. Real Seeds have instructions on their website covering saving seed from all sorts of vegetables if the idea appeals.
After growing lots of different varieties, we have settled on a cherry tomato variety called Garnet for salads and at the moment it's a toss-up between Amish Paste and the Polish Linguisa that Dani sent me seeds from for soups and sauces. I'm also experimenting this year a very early variety and some different colours. A plate of food that is a riot of colour always appeals to me.
The same applies for chiles. There's no point growing something like a Scotch Bonnet or Habanero if they're too hot for you to enjoy eating. The majority of my chiles are jalapenos, because we eat bucketloads of them, and cayenne because we dry them on strings and give them to friends and family at Christmas or blitz them into chile flakes for use in cooking. Last year I added Black Hungarian chiles which are similar to jalapenos, but start deep purple/black and eventually ripen to a beautiful glassy scarlet. It's the colour thing again
For sweet peppers I prefer pointy varieties rather than traditional bells, so always have the red and yellow Corno di Toro and after that it's more a case of what I can find that's purple, black, cream or chocolate. The more unusual colours don't really seem to be as popular and it can be tricky to find them, but scorched and peeled they can look great on pizzas for instance. Or even just raw in salads.
For preference I'd grow courgettes outdoors. Almost all the squashes are pretty boisterous plants and in a polytunnel they tend to take over. A cucumber trained up a string might work though, depending on the size of the tunnel. I'm still trying to find a variety that really works for us.
Augergines can be a bit marginal in polytunnels in my opinion. If you have a relatively warm microclimate then it might work. Here they really need a greenhouse to perform well, but we're much more exposed than many. The local town (barely two miles away) sits in a "bowl" protected by hills and despite being little more than ten metres lower than us the protection that affords allows people who live there to grow stuff that I really struggle with.
I grow everything no-dig, so in late spring before the plants go in the ground in the polytunnel I spread compost over the top of the soil (ideally my own, but every so often I have to buy in green waste compost from the council subcontractor) and then transplant everything into that. I sow hardy lettuces and mustards, chervil, dill, coriander and similar in modules in late August and transplant those straight into the polytunnel as soon as the tomatoes and peppers come out (usually late October here). Last winter was awkward and I didn't get the timing quite right, perhaps because it was so dull for so long, but for quite a few years that has kept us in salad leaves through the winter by picking one or two leaves off each plant and allowing them to regrow. The plants get removed once it's warm enough for lettuces go into the ground outdoors and then the cycle starts again.
As enrico says, make sure the cover is well fixed down. In almost twenty years I've never had a problem with my 30'x14' tunnel, but the small ones are often made to a price and may need better anchorage than you expect or than has been provided. I bought an "emergency" 6mx3m one last Summer in case we needed it for housing the chickens under cover this winter, but the winds have lifted the cover off the frame at least four times this year.
James