I have two I use a lot.

Vallejo polyurethane primers – Great range of colours, easy to spray or brush on, self levelling so that they cover well without obscuring detail.

However, they are poor if you need to sand them at all, it tends to peel rather than sand properly unless you leave it for about a week after applying.

The other is badger stynylrez. You may think this is hard to get hold of in the UK, but it is also sold under the Ultimate Modelling products brand, a UK company, Its the exact same stuff, sold under license, and is available at model shops and direct from http://www.umpretail.com

Its a lot thicker than the Vallejo product, which can make it difficult to spray if your airbrush has a smaller needle, 0.3mm and below really have trouble with it un-thinned. Like the Vallejo it’s self-leveling so you can also brush it on.

The big advantage over the Vallejo is that it dries fairly quickly, and it sands down like paint if you need to. I get on with both fine, but if I were to choose, the stynylrez is probably the one I would choose.

Got to love the army painter range of primers. I use them mostly for terrain and any large force I need a good bace colour down on. in addition I’m always looking on eBay for good deals and prices. Mostly I use Stynylrez Black, Grey and White Primer By Badger. Good place to get it in the UK is Scale Model Shop Online.

https://www.scalemodelshop.co.uk/products/paints/model-paint-auxiliaries/modelling-primer

Great Airbrush Primer, lays so well and the best on fine detail minis.

Poundland’s best prodriver grey spray primer (somebody else’s video comparing it to Halfords is linked below),

works great, costs £1 for 300ml.

the one thing I always do with all rattle cans is to test spray onto a yoghurt pot or similar just to make sure the nozzle is ok (as you do get the odd one that produces a messy spray but that’s no more of an issue than it is with something like army painter). its also worth doing when you come back to a can you’ve used before just in case you’ve got a clogged nozzle

Man, after all the comments I’ve read on this site over the years it just feels like Poundland is an absolute hobby mecca.  =)

Still using the Halfords rattlecan primer (been using it for over 30 years now). Not the cheapest, but it hasn’t let me down yet. I use either the grey primer or the Halfords Matt Black as a primer on 15mm or smaller scale minis (as you can’t afford to daub too much paint on these smaller minis without starting to obscure details).

…any else is new and trendy, and I don’t react well to change 😀

I use Vallejo for brush on primer and Stynylrez for airbrush priming. Vallejo appears a bit thicker to me so dilutes better for brush on priming. Stynylrez is already very runny and will go through the airbrush without thinning. I found Vallejo much more awkward to prime with. I nearly always prime with black.

For terrain I’ve used Halfords, Rustoleum (from Wilko if you’re UK-based) and the Poundland primer mentioned above. All were fine and my choice depended mainly on whichever was in store. Poundland sells out of primer fast round here. Not sure if @avernos can confirm but last time I looked for Halfords primer they were only pushing grey with a view to you spraying another, non-primer colour over the top. Hopefully that’s a flash in the pan and they’ll bring their usual range of coloured primers back.

@seldon9 I’m not sure about coloured primers, but the lovely red oxide is still there for all your wehrmacht needs 😀