I run my trains, so my main priority is to buy rolling stock that runs well -- couplers work properly, the cars go through switches without hopping skipping and jumping, and the locomotives function when called upon. I like to run 20-25 car trains.
My last purchase was a Lion Chief + NW2 ($229) and I'm happy with it. The great majority of my locos are Williams diesels, most purchased on sale for about $100 (Shout out to Trainworld, there). My steamers are a mix of postwar Lionel, MTH (Proto 1) and a K-Line Allegheny (TMCC).
I don't anticipate purchasing any more locomotives, though the Lion Chief + Berkshire is interesting. Current pricing on Lion Chief + has climbed to levels that still reflect increasing demand. I'll wait until the market is satiated, prices drop and then maybe consider a purchase. My 736 from 1950 still runs wonderfully.
For rolling stock, my favorite is Industrial Rail for operating performance. I run them all the time and have never had a coupler fail and they run very smoothly. Several of my MTH cars sport rubber bands to keep the couplers closed, my postwar Lionel is prized but has high rolling resistance (yes the axles are oiled) and my K-Line 6464 size boxcars and hoppers have great graphics, roll well but the couplers are close to non-functional. So, I'll be looking for used Industrial Rail cars for rolling stock. The new offerings are priced way too high for me to consider.
One thing that makes me hesitate about buying new locomotives is worrying about frying boards, DOA's, etc. I realize that we only hear about the minority of failures here and that most (Like the three I own with more than reverse boards) work fine, for me it is a lot of money to spend on something that has a degree of fragility and will be functionally obsolete (no reverse compatibility for Lion Chief app, Proto 1,2,3....TMCC, Legacy, etc).
Overall, I don't anticipate many new purchases, but I'll never say never. If I could find a nice K-Line scale Hudson at a good price (I'd be fine with conventional), I'd buy that. And I'll check out the LC+ Berk, but not at the current price.