You will get as many answers to this question as there are modelers and brands of locos.
Everyone has their favorites.
You will also get different answers for the different scales.
Here are a few things to know:
1}Quality and price are not always good bedfellows. Just because it is expensive does not mean it runs well. Example is the MTH ho locos. Look around the forum and you will see many complaints like the one above MTH's expensive $300.00 locos. Both about their quality to start, and about warrantee repairs and about paid repairs. {unfortunately}
2} Detail levels vary and are also not necessarily price dependent. Typically,the more expensive locos have better detailing, but they may not run well or last long. If you are detail oriented, don't automatically expect a good runner.
3} Some of the less detailed locos are the better runners than the more detailed ones. Strangely enough.
4}Bachmann. Many don't like them and think of them form their 60's-70's "toy train days". I personally like Bachmann. They have a few lines: basic standard, and their premium Spectrum locos. Bachmann has worked very hard to upgrade their locos form the "toy train status". Their Spectrum premium line is much more detailed and the best runners they make. They do cost a bit more than their standard line, but many first-run SPectrums become their "standard line" later on.
I have several HO Scale Bachmann DCC OnBoard locos, both standard lines, and SPectrums.And some I believe were SPectrums that are now the standard line. They are all good runners, out of over a dozen, I only have one that "growls" at slow speeds, but smooths out at higher speeds. They are all good runners, and all are decent pullers. I have not had any trouble with them in 6 years I have been in HO scale. Level of detail is far better than their "toy train" days, and the Spectrums are often highly praised for their level of detail by those who purchase them. Bachmann also has a good warrantee program should something go wrong. If they can't fix it, they will give you a new one, if no longer available, they will ofer you a few choices for replacement with a different model.
I don't do sound locos, so I cannot comment on the Bachmann DCC Sound On Board locos.
For N scale I have seen many praise Kato for their locos. But I would venture that Bachmann N scale should be as good as thier HO scales are. I have a few Bachmann N scale locos that are from the 70's that still run well on DC with little maintenance done during, oh , about 20-25 years of storage, or when brought back out to run under the Christmas tree every year sonce 6 years ago. Only 1 gives me "sparking troubles". I would hope I get as much good use out of my Bachmann HO scale locos as the old "toy train" N scalers I have.
just my thoughts, opinions and experiences and reading on the subjects. Others may vary.