Generally when your a/c doesn't keep up on hot days over 80 degrees is an indicator that it is undersized. High temps and high humidity works a/c a lot harder. On the other hand, too big of a unit will not run enough to dehumidify. You need someone to run all the calculations on your house and climate to properly size one. Some will use a general rule of thumb of 1 ton per 600 sq.ft. and some use 500 and occasionally you hear of 400 and some don't necessarily count a basement. Some can size from experience of doing the calculations all the time but get your estimates from someone who will take the time to figure yours. They look at windows, insulation, and many other factors such as the climate you live in. You didn't say where you live but the number of 100+ degree days and high humidity such as on a coast or low in a desert or mountains makes a difference.
It will still boil down to if you can live with the size you got and repair it or spend the money for a new unit. If you replace the compressor, get a newer style scroll type as opposed to the piston type. The scroll are quieter and pull less amps.
Janitrol for a rental. Ask him what he has in his house. Some people apply different standards to their rentals over what they would do their own house. Sometimes its a business decision to go with cheaper quality since they don't live there and pay the utility bills. I don't always think that makes good business sense in the long run but to each is own. I say treat it like you or your family live there and keep it in good repair like your own house or any other long term investment. Cheap repairs may result in a cheap sale price later on.
I didn't get into the electronics but usually the first test that is done is to check the amps with an ampprobe. Pulling too many amps is a sign to replace. I suppose it is a coincidence or bad luck that it went from running and pulling high amps to all of a sudden not running anymore while he was there working on it.
I don't know about this guy's reputation, but with HVAC there are a number of good quality companies with good warranties out there. See if he sells any other brands. What does he advertise at his shop and on his service truck? Even the major companies make lower grade units and price accordingly so I wouldn't rule out a Janitrol although some on this board have had bad experience with them(no one carries them in my area). The main thing is the installer, will he back up the warranty, come out when you call. Talk to them to see who you feel comfortable with, who your neighbors use, and you'll probably learn about their response time when they tell you how soon they can come out to give you your estimate. Around here, all the plumbers and electricians are usually dealers for one company they picking the HVAC company and the installer go hand in hand. The better installer may not have the brand you want and vice versa.
Good luck and post back with your other bids and where you live so we can follow through with this saga. Also add www. to the front and .com to the rear of some company names like janitrol and lennox and do some research. Try HVAC on search engine.