As such neither matter, because when the trade route is established, it grows by a fixed 1 parsec a Turn no matter the speed of the initial freighter setting it up. The route value increases in direct proportion to distance travelled after setup.
Base value of the route is Planet size and population at either end of the link, with the most important element distance of the route end to end.
So in a nutshell, a fast freighter gets it setup quicker as it gets their faster therefore dosh rolls in earlier, the further away the target planet the better, the bigger the planets at either side and the bigger the populations either side of the route the better.
If spoilt for choice go for distance, and take what you can get on the other elements, but remember that long term value is always gained by not having routes disrupted etc because of other wars - if they are you have to rebuild them, and the route value goes back to initial on restablishing one. By choosing, if at all possible by gazing in your game crystal ball (togther with that natural Strategic Brain that you have

), stable worlds that will not be zapped in third party wars before you get at them, you maximise the route returns as each route builds in value on the base value at the start of each turn.
I usually lay one on each Race, then pack one or more minor that I know I will zap later in the game with the rest, that way I'll get some money back when I raid his bank, help him defend himself before I get at him, and not give away their element of the trade if it was another Major Race. Not a lot in the latter, but every bit helps
Regards
Zy