Best Liquid Feed for Tomato Plants

What is the best tomato food, for plants growing in 9" pots, sunk into the greenhouse border please ?

I haven't grown tomatoes for a few years now, but I used to use Phostrogen, but it seems Tomorite is pretty popular now.

I'm sure you can make your own with nettles or seaweed, but I'm just looking for something easy and good.

I've recently got an allotment so will no doubt consider homemade fertilizers in the future, but just not this year. I've other things to do at the moment to get the allotment as I want.

Used tomorite for many years along with alternate weekly feeds of my homemade comfrey feed.

For comfrey sow some seed, it only takes 20-30 days to germinate and grows quickly, or  get yourself a comfrey plant. The feed or 'comfrey tea only takes 14 days to brew.
Been doing that since Beechgrove did their test of feeds and Comfrey did very well.

The Beechgrove factsheet is Factsheet 20 from September 5th 2014 that has all the details of the experiment;
https://www.beechgrove.co.uk/factsheets&cat_id=1&year=2014

I like to use one that has some seaweed in, but other than that I get the cheapest I can see 

We have maxicrop tomato on sale in our allotment shop, which is seaweed based but also has a higher proportion of potash (you want to look for the NPK ratio on the container, with the K letter higher than the others).

Don't overfeed beyond what the instructions say - it can do more harm than good, as it can stop the plant taking up other nutrients which it needs.