Got new unboxed pair of Garmin 235 from Customer Service. Should I sell it?

My advice would be to keep it and use a strap for running, if you are getting poor results with the OHR monitor. I doubt a Fitbit would be any better for the activities you describe. I have abandoned the 235 for now for 24*7 tracking and have gone back to my Fitbit Charge HR for that functionality. I do still use the 235 for Gym work and the occasional run. But again using a strap. For me OHR is not there yet for the accuracy I want for either Fitbit or Garmin.
If your one of these people that hate using straps you may get similar results with another brand, albeit with less bugs at the moment! :-). Obviously there are other users out there that seem to be getting good results with Garmin's OHR. Unfortunately you don't seem to be one of them.

I run 3 times a week for 7-12 miles per activity + mt. bike and I need a good sport watch to track all of my activities.

OK, but what specifically about those activities do you want to track? Don't just say “as much as possible, as accurately as possible, and the more the merrier,” or some such, but be specific about your requirements and criteria for fitness-for-purpose in tracking your activities.

My experience with TomTom's wearable product and customer support in the face of reported and reproducible faults leaves a lot to be desired; no FitBit wearable product is advertised as water resistant to the extent of being guaranteed not to void warranty and suffer hardware failure after a ten-minute swim in the pool; Apple Watch is a toy in my opinion, and not one I care to play with as much as I like my toys. The other brand names that come to mind are Polar and Suunto, and my preference for consideration would go to the latter (being made in Finland and all) but I know it doesn't have all the bells and whistles of a Garmin at the same price point.

OK, but what specifically about those activities do you want to track? Don't just say “as much as possible, as accurately as possible, and the more the merrier,” or some such, but be specific about your requirements and criteria for fitness-for-purpose in tracking your activities.

I want a product that works!

I want a product that works!

Works for what how? What is the objective criteria for that, that can be checked, tested and proven irrespective of how you feel? Your personal satisfaction with something is certainly not objective criteria.

Works means that the software is running properly without critical bugs or any other technical issues which cause to software be crashed.

Fair enough – and in more than three months of my owning and using my FR235, through several updates of the firmware (from 3.30 onwards) and WHR module (from 2.50 onwards), my FR235 has only ‘crashed’ and spontaneously restarted itself once. On a couple of occasions, I've run into the issue of the optical HR sensor not working at all after a reset, but this procedure (which I picked up from the collective ‘wisdom’ in this forum) resolved the issue. No doubt there are many numerous bugs and defects in the application code – for example, in setting and syncing Heart Rate Zones – but nothing I'd deem critical.

For example: if HR doesn't works

It depends on the criteria for “doesn't work”, though. I've seen many complaints from users that the optical HRM takes too long to lock on to the current HR and stabilise at the start of an activity for their liking, or that sampling for 24×7 HR tracking outside of activities are too infrequent for their liking, etc. – but that's a different kettle of fish from the LEDs in the HR sensor not coming on at all, or the HR reading getting ‘stuck’ on a figure of 66.

or device is being restarted - it is a critical bug that should be fixed immediately.

I agree on that one, and would certainly advise you not to expect a speedy resolution of that type of issue from TomTom, but I can't comment on Fitbit or the other brands in terms of their efficiency at rolling out firmware updates to address critical bugs as they surface.