The most recent stats I
saw show that the team who goes first in OT has about a 54.2% chance of winning under the current rules. What stats I can find for college ball put the second-possession team somewhere in the 52-55% win
range.
However, there is more to these stats than the simple "which team wins more". For example, college has had these rules for longer and has more teams so they have a much larger sample size both in the regular season and in bowl games. The NFLs OT rules are fairly new, and haven't been as big of an issue unless they're pertaining to the playoffs (you don't hear near as much complaint about them during the regular season since losing an OT game in the regular doesn't doesn't usually end up in your season being over). Plus, of the 8 OT games in the NFL that have been in the playoffs, the team that went first won 7 of the 8 games (I can't find a similar stat for College Ball that only breaks down bowl games) so what games we do have shows in the playoffs it's a deciding factor, but the sample size is too small to say anything definitive. Of the NFL teams that won when getting the ball first, 34% of the winning teams (and 16% of the wins overall) were on the first drive, which means that if the team who gets the ball first wins the game, more likely than not they won it without the other teams offense getting a chance.
There's also the fact that we can't draw a complete 1-to-1 comparison between the two because NCAA you play until someone scores more points, no matter how many quarters it takes, whereas even if the NFL did adopt a both teams get a chance policy it would likely still be limited to 1 possession for each team and then a sudden death shootout.
Another point that I've seen brought up regarding the current OT system is that the team that goes first is more likely to have more time and possessions to move the ball than the other team.
I also don't buy the argument that allowing both teams a defense means that defense won't matter. To avoid a tie you still need to get a stop against the other team, and if you get a stop on their very first possession then you literally just need to score a field goal and win the game. If anything it opens up a bit more of a strategic element as a coach because, if you're a team with a great defense and an average offense, you now have to weigh if you want to go first and hope you get a touchdown to put the pressure on the other team or go second, rely on your defense to get a stop and then your offense to come away with some points but not necessarily a touchdown. If you have a great offense and an average defense, do you opt to go first and just trust your defense to keep them from scoring a touchdown, or do you trust your offense enough to know that their defense won't be able to stop your offense but your defense is just good enough to stop their offense?
Watching a team in the playoffs lose in overtime without touching the ball will always leave a bad taste in my mouth no matter what team it is. We don't have to go to a full-blown college-style system but it can still be improved. Could adopt a system where whatever team wins the flip decides on either offense/defense and the other team picks a side of the field like the pre-game flip, and then if the game is still tied after each teams possession you move to a shootout-style where it goes until someone can't score or even a sudden-death first team to score wins. Either way, at least both teams gets a shot in the OT period.