My second MP2 came with EH tubes, best thing I did was change them out, they were very ordinary IMHO. You can mix and match brands for various reasons, I don't bother but others here have to get the sound they want. As WB said there's no right opinion on tube choice, it totally subjective. However, there are lots of discussions here on various tube choices, and MJMP posted some good advice for 3TM should you go that path (IIRC he like matched short plate JJs).
Of note, many tube brands are just tested and re-badged tubes from various manufacturers (e.g. Ruby JJs, Boogie STRs are mostly JJs, Groove Tubes can be various, EH tends to be sovteks etc). New Sensor (US company) bought the rights to a bunch of famous brands, Mullard (my favourite), Tung Sol etc and get reissues made (mostly the Reflector factory in Russia).
When to change is up to you, IIRC ADA recommend 2 years in MP1 and 6 months for MP2 however my experience MP1/2 with the original tubes (Chinese bottles (just has 12AX7 in red on the tube, no brand so if yours are like that they are probably the original tubes and need changing)) is they lasted a long time. They do degrade over time but very slowly so you don't tend to notice.
MJMP changes his 3TM tubes every couple of months to keep them sounding how he likes it.