I've not used Roll20 - I've used Maptools, Foundry, and gTove.
Maptools and Foundry both don't make it easy to switch att link on the fly. GTove doesn't have any character automation - it's purely maps, tokens, and dice, plus the ability to add some trackables, but no automation.
The MapTools and Foundary hard link - click the skill, and it rolls the standard stat+skill combo by standard linkage only, gets in the way. It's
exactly the most f'ing annoying part for me, the dealbreaker, especially since my favored games all have options for "any att with any skill"... despite having defaults. About 1 in 20 rolls in Alien, I was using something other than standard attribute, this was a hassle running it under Foundary using the official module.
Games I've run recently FTF include
- FFG Star Wars - hard links, explicit permission to ignore them. Also, no grid-/area-based movement,
- L5R 5e - no links, except for a very few specific types of rolls (healing/recovery.)
- Transformers - no attribute effect on rolls
- Twilight 2000 4E- hard linked, but permission to switch explicit in rules. Almost all rolls require modifications to dice sizes.
- Talisman Adventures - most skills list 2 or 3 traits which can be used for various situations, and explicitly allows calls for others when appropriate.
- Classic Traveller - no consistent rolling mechanic, let alone hard links, except in combat. And then, the mods are many.
- 2d20 system - dice not linked to abilities, but TN on dice is. # of Dice linked to expendable spends
- Star Trek Adventures - no hard links - 72 possible permutations of att and skill and whether specialty applies
- Dune: 50 permutations of drive, skill, and if in specialty
In general, I found running Alien under Foundry frustratingly constrained in terms of mechanics. Using a non-standard attribute, even when it makes sense, is a major slowdown; takes longer than using physical dice.