Retail experiences

Remember the discounts on Decathlon and Halfords via Cycling UK. It can tip the balance, esp. if you are able to collect in person.

I just bought a bike from Tredz and their service was excellent. Quick responses, plenty of flexibility, easy to get through to a human and have a conversation. 

I've got accounts with Amazon, Bike Inn, Decathlon, Fawkes, Merlin, Outdoor GB, Sigma Sports, Sport Pursuit, Trendz and Tweeks (possibly a few others as well). So usually it's just a question of who has the thing that I want, in stock, for the lowest price (including delivery).

A few years ago Decathlon were meant to be opening a store almost on my doorstep, but for whatever reason that didn't happen. Halfords is really the only bike retailer close to me, but I haven't been there in years.

I would have said Halfords are OK, if they stock the specific thing you want. Prices tend to be reasonable, and don't need to spend a fortune to get free delivery.

I tend to avoid eBay for buying anything "new". Sometimes a reputable retailer has a eBay channel selling ex-demo or items that have been returned but can't be sold as new any more, and some bargains can be had, but you have to be pretty lucky for the thing you want to be listed. I would be suspicious of anyone using eBay as their main selling channel, although maybe I'm just a cynic. 

Other than that, I tend to shop around. For widely stocked parts (e.g. Shimano components) will most likely be Sigma Sports, Merlin or Tredz. SJS are good for all the small bits you can't find anywhere else. I like Condor Cycles, although they don't have the widest range. For more niche items, start with google and see what the options are - High on Bikes, Sprockets, Wolf Cycles etc. often come through for me too. 

The only one I could add that I've used is Velozone. The range, price and service is good, although their website needs a good filtering system, so may fall down on (iv).

I'm with the other comments on the dearth of local bike shops. The last one I bought from had the stereotypical elitist bullshit so I'm not going back there. Others around me are almost all just servicing. Although there is a Balfe's not too far away which I've bought from when they've had what I'm looking for.

Used to like/use Wiggle & ProBikeKit a lot.

Since then, Sigma Sports, Merlin & SJS are worth a mention. 

BikeInn in Spain are great value if you're not in a hurry for stuff, their prices are "what you see is what you pay" and fully inclusive of any duty & tax. 

Woolly Hat Shop (https://www.bikeparts.co.uk/) I've also had good experience with.

Before anyone says "buying online is putting your LBS out of business", the only one local to me worth walking through the door is great for service jobs I can't/won't do, but doesn't really retail much in the way of parts, tools, accessories, clothing, or even bikes. So I use them when I can. The others are either crap or 30+ miles away.