While 3G networks are still doing pretty well in most parts of Europe due to HSPA+, 64QAM, dual-carrier, etc. etc., I was recently at an airport where the 3G cell covering my location seemed to have severe uplink congestion problems. Ping times were normal while only little data was transmitted in the uplink direction but immediately skyrocketed to several seconds whenever the uplink was somewhat more loaded with screen sharing and a VoIP calling. A bit of a let down.
But then I remembered that my phone I used for tethering was on LTE just a couple of minutes before and must have been redirected to 3G due to a low signal level. So I decided to lock the phone to LTE-only with an app I discovered recently. Who needs circuit switched mobile telephony anyway...!? Despite the signal level being really really low (a single signal bar was just barely shown every now and then), both uplink and downlink were much faster than what I could get over the 3G cell that was very strong in my location. Signal strength isn't everything.
Generally, I think the network operator bases thresholds for moving between network technologies are a good thing to rely on. In some cases such as this one, however, I'm glad I can make the choice myself.