I'm probably a little biased when it comes to this answer, however I've been installing TX controllers for years and I can tell you that once they are up and running (and any bugs are worked out) they run for a long time with minimal issues. I used to do alot of MCE but it seems they have their own issues anymore. I haven't installed any MCE in the past 5 years or so.
As far as proprietary stuff... just about any true Elevator tech can work on either one. Most issues can be figured out on a TX without having any special tooling. Usually we only need the Cadi/laptop to adjust the car in the beginning before turnover to the customer.

im an independent and only install non-proprietary equipment so i think im a little biased to be completely honest. i prefer non-proprietary just because i personally find it easier to work on - it depends on the manufacturer but usually there is no special tools required and if needed tech support is easy for anyone to get a hold of...so i would say MCE over TX but again thats mostly due to the fact I work on MCE and not TX...

That being said proprietary equipment does not necessarily mean trouble for you as a building manager - typically independent companies that are big enough will be able to purchase any special tools or software that is required for troubleshooting. they may have issues with tech support if needed since they are not affiliated with the company. Realistically though if the install is done correctly there shouldnt be many issues.

As i said i am an independent but i have many customers with proprietary equipment that i have been servicing for years.... the only concern i would say to be mindful of is the actual Schindler Tech that does the work - not all techs are the same but there are a few bad eggs (as there are in every company regardless) that could bug it in a way that makes your life more difficult at least the short term when a new company comes in to service it. Doesnt happen often but i have seen shady things like that happen before.

3rd party non proprietary controllers are best for all elevator companies. All service tools are provided with FULL access. They provide technical support on software and provide all upgraded versions. Parts are easily ordered and replaced with no hurdles or surprises. And everyone pays the same price for parts, boards and software. The worldwide companies will tell you their controllers are non propriety but it’s really not true. Why open yourself up to any problems down the road or to be locked in to any one or group of companies. Go 3rd party non proprietary controllers. Watch out though as a last resort they will jack up the price of the 3rd party controller. Make sure you get quotes from independent companies as well.

Always 3rd party non proprietary. Not even a question.

If you are going with a proprietary controller just make sure that you truly own it all. Otherwise you run the risk that the manufacturer will pull software/SIM cards on the way out the door. They still leave the elevator running but at some future point it may "lock up" and then you are at their mercy.

How old is your existing equipment? What type of equipment are you running now? Controller, selector, door operator, door equipment, fixtures? Hydro or traction? How many floors?

28 y.o, US Elevator MP1220, GAL MOH door operator, traction, 11 stops (not sure on the selector, door equipment, or fixture - used to be soft touch II)

Geared or gearless machine? 350 fpm?

geared Hollister Whitney. 53 B.S.. 350 fpm.

3rd party non proprietary all the way, it doesn't matter if a Schindler will run 'fine' for a while with limited 'bugs'. Eventually, down the line, it will bite you back in the ass, and you'll be forking out big bucks for parts and repairs.

Find a good, big local independent and even go view some of their installs and see for yourself how they ride ECT..

I would advise against the TXR5. As mentioned there is a sim chip that can be removed which will take away diagnostic functions. Also if the drive fails it will require Schindler to come back to load software with a proprietary tool. Some of the larger companies have tools to get around the SIM chip but I’m not aware of anyone else that can load the drive software other than Schindler.

So if it was just between the 2 I would say MCE all day. But I would also highly recommend smart rise and GAL as well for non proprietary controls. I would also recommend getting other bids.

Can that be done through Adams software?
https://www.adamselevator.com/pdf/software_upgrades.pdf

You can purchase some software directly from Adams but you would still need a proprietary tool to load software and set up the drive.

I have had the pleasure of working on both companies controllers. My biggest issue is the lack of troubleshooting access on the TX' s and like Abe said, if software is needed for any future upgrades, your gonna pay through the nose as well as waiting on Schindler to get around to it with the tool they use. They bring an Sim card with them so they can load and adjust them remove it when they are done. The TX' s are a very good running system once setup right but MCE or GAL have alot more freedom for changes and add ons.
Hope this helps!