On MV gear, ABB in the past has had issues with racking mechanisms. Siemens has typically had door alignment issues. Both cause maintenance irritation. Make sure the ABB trip units have the functionality and capability that your looking for as there can be a huge variation between manufacturers, GE's and Siemens IMO are not worthy. The only other thing, is make sure the gear is either ANSI only rated or as a minimum dual ANSI/IEC rated.
A good indication right now is schedule. Everybody is pretty much quoting 24 weeks on LV power switchgear due to factory loading and engineering. Even if you have LD's in place in the contract, and they max them out, they will have no incentive to get the gear to your site when you need it. Make sure there is plenty of time scheduled for drawing prep, drawing review, manufacturing, shipping, and installation. The tighter the schedule the more prone to delays.
As mentioned, do not let the manufacturer include his BOM (Bill of Materials) as part of the contract, or allow wording to refer to them as part of the contract. Manufacturers do this to qualify there bid without having to take a bunch of exceptions, becasue exceptions are undesireable. Then it becomes your responsibility to review, the each quote in minute detail, bid prior to awarding contract.