TM engines start faster & more traditionally (TOT up to 750 ish), P&W take ages before the TOT starts to register and you wonder if they've actually lit up, as it's so benign - but they all get there in the end.
As has been said, TMs
much cleaner than the P&Ws.
The biggest difference (certainly with TM's power by the hour (PBH) or P&W's equivalent Eagle programme) is that you
own your P&Ws. It means that when one is removed for unexpected maintenance, you'll get a loaner, which you're then obliged to swap back for your "
own" engine when they've fixed the problem, almost as soon as you've got it back, or you'll pay. TM will just replace your engine (the old one goes back into the pool when it's fixed) - so one change rather than two. For some, this may be good news (as you know how you've looked after your own engines), for others it could be more annoying - certainly if they're fitted in a 902! (yes, I know we're looking at a 135!)
P&W require a daily rinse, TMs every 20 hours, unless when operating in saline environment (recently re-defined), when it's daily. You can do a hot or cold rinse with TMs, cold only for P&W.
On a daily basis, it's a lot easier to put oil in the TM, as you can do it standing on the skid - you need to be more of an acrobat to get it into the P&W, as you're almost hanging off the blades!
We've had TMs for 6 years, 6500 hrs - fantasically reliable, start together straight away every time (with 40 AH battery). PBH, admitedly, but never had a spares problem and only shut one down once, in that time (oil loss due to bearing seal failure). Don't notice any difference in power available betwen the two.
If it were my choice, I'd go for TMs again as they're so much cleaner; start faster & more obviously; & are easier to top-up oil. Pilot's viewpoint, mind, not engineers - they might see it differently?!
EDIT to explain Coconutty's humour: if you're not familiar with British children's shows in Prague, take a look at
The Sooty Show | The Official Sooty Website | Home of Sooty, Sweep and Soo! 